Original English string is about "custom emojis" and therefore a better translation is "emojis personalizados". Note that "emoji" is a neologism accepted and understood in Spanish (see e.g. Spanish Wikipedia).
* strings: Add spanish translations
I kept more or less the same length as the original english translations so everything should fit, although I'm unable to test them at the moment.
For every string I wasn't sure how to translate I checked it against the web interface equivalent from mastodon.social
For every alert or information provided by the app I used a polite verb form, while keeping casual ones for interactions between users.
* strings: Add missing spanish translation
