diff --git a/td/generate/scheme/td_api.tl b/td/generate/scheme/td_api.tl
index c8a90b284..3cd0c63e2 100644
--- a/td/generate/scheme/td_api.tl
+++ b/td/generate/scheme/td_api.tl
@@ -3133,9 +3133,12 @@ getLanguagePackInfo = LanguagePack;
 //@description Returns strings from a language in the used language pack by their keys @language_code Language code of strings to return @keys Language pack keys of strings to return; may be empty to get all available strings
 getLanguagePackStrings language_code:string keys:vector<string> = LanguagePackStrings;
 
-//@description Adds or changes a custom language to the used language pack @info Information about the language. Language code should start with 'X' @strings New language pack strings
+//@description Adds or changes a custom language to the used language pack @info Information about the language. Language code must start with 'X' @strings New language pack strings
 setCustomLanguage info:languageInfo strings:vector<LanguagePackString> = Ok;
 
+//@description Sets new value for a string in a custom language in the used language pack @language_code The code of previously added custom language, must start with 'X' @string New language pack string
+setCustomLanguageString language_code:string string:LanguagePackString = Ok;
+
 //@description Deletes all information about a language in the used language pack. Currently used language can't be deleted @language_code Language code of a language to delete
 deleteLanguage language_code:string = Ok;
 
diff --git a/td/generate/scheme/td_api.tlo b/td/generate/scheme/td_api.tlo
index c816c30a6..d7ea24417 100644
Binary files a/td/generate/scheme/td_api.tlo and b/td/generate/scheme/td_api.tlo differ
diff --git a/td/telegram/AnimationsManager.cpp b/td/telegram/AnimationsManager.cpp
index 63b405cc3..bc3e5f6e7 100644
--- a/td/telegram/AnimationsManager.cpp
+++ b/td/telegram/AnimationsManager.cpp
@@ -656,7 +656,7 @@ void AnimationsManager::remove_saved_animation(const tl_object_ptr<td_api::Input
   // TODO invokeAfter
   auto file_view = td_->file_manager_->get_file_view(file_id);
   CHECK(file_view.has_remote_location());
-  CHECK(file_view.remote_location().is_document());
+  CHECK(file_view.remote_location().is_document()) << file_view.remote_location();
   CHECK(!file_view.remote_location().is_web());
   td_->create_handler<SaveGifQuery>(std::move(promise))->send(file_view.remote_location().as_input_document(), true);
 
diff --git a/td/telegram/LanguagePackManager.cpp b/td/telegram/LanguagePackManager.cpp
index def71aa9d..be95e9f10 100644
--- a/td/telegram/LanguagePackManager.cpp
+++ b/td/telegram/LanguagePackManager.cpp
@@ -628,7 +628,7 @@ void LanguagePackManager::save_strings_to_database(Language *language, int32 new
     return;
   }
   auto old_version = load_database_language_version(kv);
-  if (old_version >= new_version && (old_version != -1 || new_version != -1)) {
+  if (old_version > new_version || (old_version == new_version && strings.empty())) {
     LOG(DEBUG) << "Language version doesn't increased from " << old_version;
     return;
   }
@@ -662,7 +662,7 @@ void LanguagePackManager::on_get_language_pack_strings(
   bool is_version_changed = false;
   int32 new_database_version = -1;
   vector<std::pair<string, string>> database_strings;
-  if (language == nullptr || (language->version_ < version || !keys.empty())) {
+  if (language == nullptr || language->version_ < version || !keys.empty()) {
     if (language == nullptr) {
       language = add_language(database_, language_pack, language_code);
       CHECK(language != nullptr);
@@ -792,56 +792,62 @@ void LanguagePackManager::on_failed_get_difference(string language_pack, string
   }
 }
 
+Result<tl_object_ptr<telegram_api::LangPackString>> LanguagePackManager::convert_to_telegram_api(
+    tl_object_ptr<td_api::LanguagePackString> &&str) {
+  if (str == nullptr) {
+    return Status::Error(400, "Language strings must not be null");
+  }
+
+  string key;
+  downcast_call(*str, [&key](auto &value) { key = std::move(value.key_); });
+  if (!is_valid_key(key)) {
+    return Status::Error(400, "Key is invalid");
+  }
+  switch (str->get_id()) {
+    case td_api::languagePackStringValue::ID: {
+      auto value = static_cast<td_api::languagePackStringValue *>(str.get());
+      if (!clean_input_string(value->value_)) {
+        return Status::Error(400, "Strings must be encoded in UTF-8");
+      }
+      return make_tl_object<telegram_api::langPackString>(std::move(key), std::move(value->value_));
+    }
+    case td_api::languagePackStringPluralized::ID: {
+      auto value = static_cast<td_api::languagePackStringPluralized *>(str.get());
+      if (!clean_input_string(value->zero_value_) || !clean_input_string(value->one_value_) ||
+          !clean_input_string(value->two_value_) || !clean_input_string(value->few_value_) ||
+          !clean_input_string(value->many_value_) || !clean_input_string(value->other_value_)) {
+        return Status::Error(400, "Strings must be encoded in UTF-8");
+      }
+      return make_tl_object<telegram_api::langPackStringPluralized>(
+          31, std::move(key), std::move(value->zero_value_), std::move(value->one_value_), std::move(value->two_value_),
+          std::move(value->few_value_), std::move(value->many_value_), std::move(value->other_value_));
+    }
+    case td_api::languagePackStringDeleted::ID:
+      // there is no reason to save deleted strings in a custom language pack to database
+      return make_tl_object<telegram_api::langPackStringDeleted>(std::move(key));
+    default:
+      UNREACHABLE();
+      return nullptr;
+  }
+}
+
 void LanguagePackManager::set_custom_language(string language_code, string language_name, string language_native_name,
                                               vector<tl_object_ptr<td_api::LanguagePackString>> strings,
                                               Promise<Unit> &&promise) {
-  if (!is_custom_language_code(language_code)) {
-    return promise.set_error(Status::Error(400, "Custom language code must begin with 'X'"));
-  }
   if (!check_language_code_name(language_code)) {
     return promise.set_error(Status::Error(400, "Language code name must contain only letters and hyphen"));
   }
+  if (!is_custom_language_code(language_code)) {
+    return promise.set_error(Status::Error(400, "Custom language code must begin with 'X'"));
+  }
 
   vector<tl_object_ptr<telegram_api::LangPackString>> server_strings;
   for (auto &str : strings) {
-    if (str == nullptr) {
-      return promise.set_error(Status::Error(400, "Language strings must not be null"));
-    }
-    string key;
-    downcast_call(*str, [&key](auto &value) { key = std::move(value.key_); });
-    if (!is_valid_key(key)) {
-      return promise.set_error(Status::Error(400, "Key is invalid"));
-    }
-    switch (str->get_id()) {
-      case td_api::languagePackStringValue::ID: {
-        auto value = static_cast<td_api::languagePackStringValue *>(str.get());
-        if (!clean_input_string(value->value_)) {
-          return promise.set_error(Status::Error(400, "Strings must be encoded in UTF-8"));
-        }
-        server_strings.push_back(
-            make_tl_object<telegram_api::langPackString>(std::move(key), std::move(value->value_)));
-        break;
-      }
-      case td_api::languagePackStringPluralized::ID: {
-        auto value = static_cast<td_api::languagePackStringPluralized *>(str.get());
-        if (!clean_input_string(value->zero_value_) || !clean_input_string(value->one_value_) ||
-            !clean_input_string(value->two_value_) || !clean_input_string(value->few_value_) ||
-            !clean_input_string(value->many_value_) || !clean_input_string(value->other_value_)) {
-          return promise.set_error(Status::Error(400, "Strings must be encoded in UTF-8"));
-        }
-        server_strings.push_back(make_tl_object<telegram_api::langPackStringPluralized>(
-            31, std::move(key), std::move(value->zero_value_), std::move(value->one_value_),
-            std::move(value->two_value_), std::move(value->few_value_), std::move(value->many_value_),
-            std::move(value->other_value_)));
-        break;
-      }
-      case td_api::languagePackStringDeleted::ID:
-        // there is no reason to save deleted strings in a custom language pack to database
-        break;
-      default:
-        UNREACHABLE();
-        break;
+    auto r_result = convert_to_telegram_api(std::move(str));
+    if (r_result.is_error()) {
+      return promise.set_error(r_result.move_as_error());
     }
+    server_strings.push_back(r_result.move_as_ok());
   }
 
   // TODO atomic replace
@@ -855,11 +861,45 @@ void LanguagePackManager::set_custom_language(string language_code, string langu
   auto &info = pack->language_infos_[language_code];
   info.name = language_name;
   info.native_name = language_native_name;
-  pack->pack_kv_.set(language_code, PSLICE() << language_name << '\x00' << language_native_name);
+  if (!pack->pack_kv_.empty()) {
+    pack->pack_kv_.set(language_code, PSLICE() << language_name << '\x00' << language_native_name);
+  }
 
   promise.set_value(Unit());
 }
 
+void LanguagePackManager::set_custom_language_string(string language_code,
+                                                     tl_object_ptr<td_api::LanguagePackString> str,
+                                                     Promise<Unit> &&promise) {
+  if (!check_language_code_name(language_code)) {
+    return promise.set_error(Status::Error(400, "Language code name must contain only letters and hyphen"));
+  }
+  if (!is_custom_language_code(language_code)) {
+    return promise.set_error(Status::Error(400, "Custom language code must begin with 'X'"));
+  }
+
+  if (get_language(database_, language_pack_, language_code) == nullptr) {
+    return promise.set_error(Status::Error(400, "Custom language not found"));
+  }
+
+  string key;
+  if (str != nullptr) {
+    downcast_call(*str, [&key](auto &value) { key = value.key_; });
+  }
+
+  auto r_str = convert_to_telegram_api(std::move(str));
+  if (r_str.is_error()) {
+    return promise.set_error(r_str.move_as_error());
+  }
+
+  vector<tl_object_ptr<telegram_api::LangPackString>> server_strings;
+  server_strings.push_back(r_str.move_as_ok());
+
+  on_get_language_pack_strings(language_pack_, language_code, 1, true, {std::move(key)}, std::move(server_strings),
+                               Auto());
+  promise.set_value(Unit());
+}
+
 void LanguagePackManager::delete_language(string language_code, Promise<Unit> &&promise) {
   if (!check_language_code_name(language_code)) {
     return promise.set_error(Status::Error(400, "Language code name is invalid"));
diff --git a/td/telegram/LanguagePackManager.h b/td/telegram/LanguagePackManager.h
index 83f3bf5a6..262d958bd 100644
--- a/td/telegram/LanguagePackManager.h
+++ b/td/telegram/LanguagePackManager.h
@@ -60,6 +60,9 @@ class LanguagePackManager : public NetQueryCallback {
   void set_custom_language(string language_code, string language_name, string language_native_name,
                            vector<tl_object_ptr<td_api::LanguagePackString>> strings, Promise<Unit> &&promise);
 
+  void set_custom_language_string(string language_code, tl_object_ptr<td_api::LanguagePackString> str,
+                                  Promise<Unit> &&promise);
+
   void delete_language(string language_code, Promise<Unit> &&promise);
 
  private:
@@ -105,6 +108,9 @@ class LanguagePackManager : public NetQueryCallback {
   static td_api::object_ptr<td_api::languagePackStrings> get_language_pack_strings_object(Language *language,
                                                                                           const vector<string> &keys);
 
+  static Result<tl_object_ptr<telegram_api::LangPackString>> convert_to_telegram_api(
+      tl_object_ptr<td_api::LanguagePackString> &&str);
+
   void inc_generation();
 
   static bool is_valid_key(Slice key);
diff --git a/td/telegram/Td.cpp b/td/telegram/Td.cpp
index 714a940e1..32dce6921 100644
--- a/td/telegram/Td.cpp
+++ b/td/telegram/Td.cpp
@@ -3268,6 +3268,7 @@ bool Td::is_preauthentication_request(int32 id) {
     case td_api::getLanguagePackInfo::ID:
     case td_api::getLanguagePackStrings::ID:
     case td_api::setCustomLanguage::ID:
+    case td_api::setCustomLanguageString::ID:
     case td_api::deleteLanguage::ID:
     case td_api::getOption::ID:
     case td_api::setOption::ID:
@@ -6053,6 +6054,14 @@ void Td::on_request(uint64 id, td_api::setCustomLanguage &request) {
                std::move(promise));
 }
 
+void Td::on_request(uint64 id, td_api::setCustomLanguageString &request) {
+  CHECK_IS_USER();
+  CLEAN_INPUT_STRING(request.language_code_);
+  CREATE_OK_REQUEST_PROMISE();
+  send_closure(language_pack_manager_, &LanguagePackManager::set_custom_language_string,
+               std::move(request.language_code_), std::move(request.string_), std::move(promise));
+}
+
 void Td::on_request(uint64 id, td_api::deleteLanguage &request) {
   CHECK_IS_USER();
   CLEAN_INPUT_STRING(request.language_code_);
diff --git a/td/telegram/Td.h b/td/telegram/Td.h
index de4c699bd..6efec72bb 100644
--- a/td/telegram/Td.h
+++ b/td/telegram/Td.h
@@ -769,6 +769,8 @@ class Td final : public NetQueryCallback {
 
   void on_request(uint64 id, td_api::setCustomLanguage &request);
 
+  void on_request(uint64 id, td_api::setCustomLanguageString &request);
+
   void on_request(uint64 id, td_api::deleteLanguage &request);
 
   void on_request(uint64 id, td_api::getOption &request);
diff --git a/td/telegram/cli.cpp b/td/telegram/cli.cpp
index 70dde59f6..992afd885 100644
--- a/td/telegram/cli.cpp
+++ b/td/telegram/cli.cpp
@@ -1786,6 +1786,25 @@ class CliClient final : public Actor {
 
       send_request(make_tl_object<td_api::setCustomLanguage>(
           make_tl_object<td_api::languageInfo>(language_code, name, native_name), std::move(strings)));
+    } else if (op == "sclsv" || op == "sclsp" || op == "sclsd") {
+      string language_code;
+      string key;
+      string value;
+
+      std::tie(language_code, args) = split(args);
+      std::tie(key, value) = split(args);
+
+      tl_object_ptr<td_api::LanguagePackString> str;
+      if (op == "sclsv") {
+        str = make_tl_object<td_api::languagePackStringValue>(key, value);
+      } else if (op == "sclsp") {
+        str = make_tl_object<td_api::languagePackStringPluralized>(key, value, string("One\0One", 7), "Two", "Few",
+                                                                   "Many", "Other");
+      } else {
+        str = make_tl_object<td_api::languagePackStringDeleted>(key);
+      }
+
+      send_request(make_tl_object<td_api::setCustomLanguageString>(language_code, std::move(str)));
     } else if (op == "dl") {
       send_request(make_tl_object<td_api::deleteLanguage>(args));
     } else if (op == "go") {