Grammar correction in de.json

See merge request !90

I18n: Update Czech translation 🇨🇿

See merge request !88

Update Polish translation

See merge request !83

Remove national flags from language selector and add accessibility info

See merge request !82

Add Cuckoo+ in the Apps page

See merge request !71

Improve locale detection

Closes #23

See merge request !87

Add Mastonaut to Desktop apps

See merge request !80

Change Fedilab Logo

See merge request !84

Fix Russian locale

See merge request !86

Further proofreading of new translations shown some mistakes, such as:

- usage of plural argument, when source for it is a string
- unpleasant joke about mispill which is fixed to re-draft now
- awkward mistake in title of the page
- some other mistakes

On top of that, brand kit button does not fix and its container
is too small. I've found fixes for locale, so put one for Russian
just to fix this case (hope it works).

This allows users to give links such as joinmastodon.org/?lang=fr to
their friends, who on visit will be seeing, in this case, French
version of the site, but users can also supply any other locale there:
if locale is not found, it will fallback to auto-detection or English.

We could have also added a copy of index.html page for every locale,
but I'm not sure how to do this, so will leave it as is.

All locales in `defaultLocales` are supported and can be selected
by the end-user, so we don't have any reasons to fill them in manually.

This commit changes so that for every locale in `defaultLocales`, an
element containing its name will be pushed to `supportedLocales` array.

Fixes #23

Improve Russian locale

See merge request !85