Talking off the top of my head but
- You just paste the enriched text, i.e. text with [b][\b] tags and so on, in the Language tab, only chaging the plain text. Bubble will automatically interpret the enriched formatting when substituting the AppText version.
- You either account for it by preparing a proper responsive behaviour of everything for slightly longer texts OR reword Spanish translations so they are shorter, even if you have to slightly change the message.