Localize according to the Accept-Language header

[martinpopel]

This issue should be discussed first, before implementing.

Our users can be Czech or Ukrainian, but most often they cannot speak/understand the other language.

• We should localize the consent pop-up message or provide it in both Czech and Ukrainian (it is already done in the info/settings page, but not in the pop up). Now Ukrainian users may click on "Souhlasím" without actually understanding the consequences. I think this is a high-priority issue.
• We can localize the "About us" tooltip and open the appropriate CS/EN/UK translation of the consent in the info/settings page by default. This is a low-priority issue.
• We can set the initial translation direction based on user/browser preferences, expecting that Czech users mostly want to use cs->uk and Ukrainians uk->cs. Of course, once the user switches the languages, this setting is stored in the local storage and used next time - this behavior should be preserved. Note that Language detection and warning that the input is in Russian #25 is about a related, but different issue (suggesting to switch the translation direction after the users inserts some text, while this issue is about the appearance before any input).

I am not sure what is the most reliable way to detect user language preferences:

• the Accept-Language HTTP header
• the navigator.language or window.navigator.languages property

Of course, there could be Ukrainian users using a (borrowed) device with Czech localization.