Add language/locale settings

[ShGKme]

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Is your feature request related to a problem? Please describe.

Currently app's language/locale is set from the system preferences.

A user may want to have Talk settings different from the system like with theme.

Describe the solution you'd like

Add a setting with:

• Use system (LANG)
• Use account setting (LANG)
• list of all supported languages

Describe alternatives you've considered

Ignore.

Additional context

• Related issue: Configure languages used for spell checking #771