feat(store/languages): as signal

[rbalet]

Current behavior

Actually, we're able to add/remove language from the service, but as this is a simple variable, we cannot do much with it.

Expected behavior

it being a signal

What is the motivation / use case for changing the behavior?

1. Being able to subscribe to the signal change with a computed
2. Will help team using the library having a single source of through, regarding which languages are used.

How do you think that we should implement this?

1. change it into a $languages signal
2. deprecate languages

[rbalet]

@CodeAndWeb I'll do a PR and we can discuss about it later if you're ok