As a 35M, is there any benefit to having more than one second language under your belt?

I’m a 35M who came in prior to the requirement. I was supposed to do Egyptian Arabic. There is no military benefit other than money if you can get the right score. You will not use your language on missions. You can only run operations in English, however if you get out a second language is always a bonus. I speak 3 other languages, but I don’t use them for work.

The following is true Army-wide:

Short answer: No. You won't get paid for knowing Spanish *unless* it's your "Control Language" (Which it's not, as you're learning Mandarin). You won't be paid just for knowing and DLPT-ing in Spanish. It is good to have it on your ERB though.

If you know any of languages in the "A" or "B" category in the link here at a 2/2 level or higher, then you get paid regardless if it's your Primary Language:
US Army Foreign Language Strategic List (13 November 2019): https://www.hrc.army.mil/asset/21086

Pay scale according to language ability and language level on the above memo (Table 4-2):https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/r11_6.pdf

Yes, yes, yes, YES!

To be perfectly honest, Spanish is unlikely to be useful. But unlikely is not the same as impossible. But any second or third or fourth or 27th language CAN be helpful.
Most of the times, even if you are proficient in a language, you will still use a native speaker to interpret because they get all of the idioms and local turns of phrases and such that your text-book speech may not pick up. BUT knowing the language is EXCEPTIONALLY beneficial because A) you can follow the conversation better, which helps you respond quicker and more fluidly B) if the interviewee does not know you speak the language, they may speak more freely, assuming (or even directing) the interpreter not to translate something and you can catch interesting tidbits C) if the interviewee knows you DO speak the language, they are more likely to speak to *you* rather than the interpreter, and this *can* help build rapport D) if the interpreter knows you speak the language, it keeps them honest, and E) if the interpreter DOESN'T know you speak the language, it is a great way to vet them.
As I said, Spanish is unlikely to be useful for most of your missions, but there is a chance you can be working somewhere for SOUTHCOM where it might come in handy, or even in a Joint environment with Spanish NATO forces. Not likely, but possible. And if you know Spanish, start learning French. While they are not at all the same language, knowing one *does* make it easier to learn the other. And French is VERY useful in Africa.