Add i18n and l10n

[opensourcecheemsburgers]

Decide what to use. Perhaps fluent or rust-i18n.

Strings

• [x] Replace all hardcoded strings and set up translation guide on Github.
• [x] Replace invidious hardcoded strings with locally generated strings.
• [x] Replace invidious hardcoded numbers with locale number strings.

[opensourcecheemsburgers]

I have decided to go with Fluent for now.

[opensourcecheemsburgers]

Nvm, Fluent was too verbose and overkill.