Most business in Puerto Rico is conducted in Spanish. English appears where it appears, often with mainland suppliers, off-island head offices, and certain corporate functions, and a system configured as though English is the default will produce customer-facing messages that read as though they were written for somewhere else.
Language belongs on the contact
Record it at the point of first contact, where the answer is obvious and takes a second. Then let every outbound message key off that field: sequences, acknowledgements, quotes, reminders, and the automatic confirmation a customer receives after enquiring.
That last one matters more than people expect. A customer who writes to you in Spanish and receives an automated acknowledgement in English has learned something about your business in the first thirty seconds, and it is not what you wanted them to learn.
Keep both versions of a template together
The common approach is to build two separate campaigns, one per language. It works for a month. Then somebody improves the Spanish version, nobody updates the English one, and within a quarter the two are saying different things. Holding both language versions of a single template together means the sequence is maintained once and delivered correctly, which is the only version of this that survives a busy year.
Check the small things during a trial
Accented characters and the special characters used in Spanish should render correctly in every place a name or a message appears: in the interface, in an email, in a text message, on an exported file, and on a printed quote. This is straightforward to test and occasionally reveals a system that handles it badly, which is much better to discover in week one than after migrating three thousand records.