The value of the lang_code parameter depends on the language of the Telegram application. It doesn't matter which keyboard layout is enabled.
For example:
In Telegram, the default language is Russian.
I am writing a message in English. lang_code = ru
IMPORTANT: After changing the language of telegrams, you need to wait 3-7 minutes until the setting is updated on the telegram server (I think so). Because if you write messages immediately after changing the language of the application, it will display the first language.