[Tasks] Localization

## Tasks
**Localize**
- [x] #55
- [x] #56
- [x] #57
- [x] #58
- [x] #77
- [x] #78
- [ ] #155
- [x] #247
- [x] #277

**Docs**
- [x] #249

**Dev**
- [x] #250
- [ ] #251
- [x] #252

## Localization status

| Language | Language Code | Translated | Validated |
|--------------------|---------------|------------|---------------|
| English | `en` | 100% | ✔︎ (@philipbrembeck Philip) |
| German | `de` | 100% | ✔︎ (@philipbrembeck Philip, @fastrcloud Max) |
| French | `fr` | 100% | ✔︎ (Léa) |
| Spanish | `es` | 100% | ✘ |
| Polish | `pl` | 99% | ✔︎ (@lwojcik)
| Czech | `cz` | 100% | ✔︎ (@MichalBryxi)

## Help us with localization
Localizations can be found in `src/locales`.
All language files are in a `[countrycode].json` file. Please check our translations if there is already one localization file available in the language you are speaking.
Otherwise, please create a new json file and duplicate the contents of the `en.json` file and translate the strings to your language.