Manual change of language causes issues

Description

After changing the language in Account -> Preferences variables don't display properly :

Plus, if Ctrl+F5 is used on any page the language switch back to initial language. Same if browser history is deleted.

Steps to Reproduce

1. Go to Account -> Preferences
2. Select another language
3. Check the variables display (in the footer for instance)
4. Press Ctrl-F5 (switch back to initial language)

Expected behaviour:

• Variables should be displayed properly after a manuel language change.
• Language choice should be saved in my account, even if i use an other browser

Actual behaviour:

• Variables aren't properly displayed.
• Language change isn't permanently saved.

Reproduces how often:

Every time.

Versions

• On Mobilizon.fr 1.0.0
• Tested on Firefox 82.0 (64 bits) and Chrome 86.4.4240.111 (Build officiel) (64 bits)

Additional Information

[Any additional information, configuration or data that might be necessary to reproduce the issue.]