I admit this one has me puzzled. Latin, as in the language, or as in latin America etc is "unknown". Latina and latino do exist as rares.
*I* normally spell it with a small l. Is it because it's a proper noun? In the case of latin America does such a part of speech as a "proper adjective" exist? If not, and if it still must be capitalised, then as its discoverer I hereby name this portion of grammar the "2 Tanners Proper Adjective" (c)(TM). All future use of this part of speech is subject to a licencing fee of 1c (1d for British use and 0.01 Euro for Eurozone use).
Now THAT'S what I call capitalisation!!