Help with this translation!
 

I was tasked with translating some text for a flyer, and one of the phrases is "altar for black lives," and I wasn't sure which terms would be the most commonplace and not at all offensive. Thank you very much!:)

Since we are not professional translators here, just a community of language learners, you may want to seek out a professional translation service for assistance.

But, to give you some ideas of the possibilities for producing your own translation, I did a quick search. More context or information gets you closer to the correct translation than I can.

An altar can mean different things to different people; so can a monument, statue, pile of rocks, or a pillar. Only you know what the actual altar is or what it might represent, so just choose the right term. You'll most likely want to come up with a definite article (the) that agrees in gender and number with the term you decide to use.

'Black lives' is translated as 'vidas negras' all over the place. Its use doesn't meet with disapproval, as far as I saw. Again, you'll need to come up with a suitable definite article for this phrase.

Determining which preposition to insert after the topic (the altar) will be your last task. Both por and para can be translated as 'for', but aren't always interchangeable.
Use por to indicate that the altar benefits someone, stands in for (in the place of or instead of) someone, is in favor of someone, is because of something, is intended for someone, or is in honor of someone.
Use para when describing the altar's purpose, or when the altar is intended or designed for someone, is appropriate to someone, or is a standard for comparison.

Either preposition may be used to express 'in order to save or preserve'.