Since original thread is closed and I consider this as a bug, I can't be satisfied with the conclusion.
https://forums.garmin.com/showthread.php?75471-Language-bug-mobile-app-X-website
DOUG996INK:
"In version 2.0.1 of the Android app, upon successful sign-in, the code updates your language on Connect Web to the "language" the Android device is currently set to. The reason for this is because when the mobile app requests data from your Connect account, some of that data arrives already translated, according to the "language" set in Connect. So, imagine, that the language is NOT updated upon sign-in. So now you have Portguese set as the language in Connect, and the "US/english" locale set on your Android device. On the "activity details" screen, for example, some labels and text would be in Portguese, and others would be be in English. We actually saw this happen during development, and decided it was best to keep the languages synced up. I see your delima though."
This is simply bad design decision, which messes up many non-US people. I also have phone with Czech locales, but use Garmin Connect web in English ... just because your translations is poor :mad: . Primary problem is that you allow people to change language on web, but don't allow to choose language in mobile application and automatically :mad: change language in one-way. So the language chooser in GC is useless in long term. Moreover if I look on current Garmin Connect Modern in Czech, it's mixed English and Czech -- thing you wanted to avoid in mobile app. happens on web. Because I don't like Garmin Connect in language you are automatically switching me to during every sync, I'm always reverting GC to English on each visit and this messes me up much much more. Then your try to get data in phone locales is ruined.
I dont' care that your API is broken and can't answer with data in particular locales. It's still bug.
Please don't ask people to change whole phone locales only because developers of one app. Thanks for fixing this soon!