The appliaction Garmin Connect Mobile follows the Android standards, hence you can change the laguage in the settings of Android OS. If your OEM version of Android, or a 3rd party app allows a per-application language settings, or specific settings for individual features like the audio input, then you can use it, of course, too. However, all of that, are settings out of the control fo the Garmin Connect app.
Thanks for the feedback, I thought that developer can put a settings into the app to change language if an user would like to have a different language from the system one.
I would like to do only to send to the beta team of my Garmin device screenshot of the app in English.
No problem, I will send them in my language hoping they will understand.
You can eaisily temporarily change the language to English in Android settings, make the screenshot, and then setting it back to your language. However, if you contact your local support, they will certainly have no problems with your own language You can also try posting your problem here on the forum, first. Most of the problems can be solved quickly by other, more experienced users.