Possibly a tricky question but it meant to sound interesting. There is always exeptions to rules (I know) but I bumped into a "CPO" (without mil/LE background) who assured me that he was working for an extended period of time in Spain without speaking the language. Regardless, if I believe him or not, the posibilities to act as a CPO in another country would have to be limited just for that reason. Possibly the title should have been "How to learn another language ASAP" to avoid upsetting anyone.
Without getting into detail why I think I'm "qualified" and know something about it, "How did I learn another language ASAP"?
Be aware (to the newbies) that CPOs are like any other industry/sector (Doorman, Police, etc.). You have slow, dumb, rude and fat ones as well as the highly skilled ones. Most CPOs (not HE) I have meet, did actually not speak a second language unless they were from another country. Hence being fluent in another language will increase your employment opportunities. As a second language I would focus on a language from my own language group. What I mean is, lets say you are english, than learning arabic or mandarin as a second language can be a mayor challenge, as everything is different (writing, spelling, pronounciation, etc.). I would focus on languages "more similar" in grammar, such as german, as it comes from the same language group as english does. However, english has a healthy intake of latin structure and so most schools try to teach (to limited extend), french. French is from the same language group as romanian and so romanians find it easy to learn French, Spanish, etc.
Most recent conflicts/unrest since WW2 emerge(d) in South America, Africa and the Middle East which narrows it down to Spanish (Portugese for Brazil), French for the mayority of Africa and Arabic for the middle east and beyond. In this situation a brit should focus first on french maybe spanish if applicable. In my case it did not apply and I had no choice but to study a language beyond my language group.
So, as a middle aged guy how did I get around, learning (very) basic french within a month+?
I bought myself (by now several times) a phrase book. A simple one, without the fancy pictures and other distractors which focus on "fun-study".
I learned about 10-20 (depending how motivated you are) most simple and short phrases. I checked internet sources for pronounciation and polished my accent, closing my eyes using my hearing-memory I repeated and repeated. I then learned the crucial words out of these sentences (not all). This allowed me to recognise grammar as well as possibly related themes within the phrase book.
Good phrase books are basic and simplyfied so you can easily use it in the field, not like a dictionnary where you need 30'+ mins to translate a sentence. Hence information was repetitive and I made a few more links between new words (however I tried to avoid overload and kept it basic). I learned useful sentences involving rather broad meaning words such as; "where is this..." and "where is that...", "thank you", "Nice to meet you", etc. Instead of swear words, etc :)
And so I had an early 15-20 minutes study in the morning, possibly a brief look into the phrase book at lunch and a 20 minutes revision before sleep.
*Apart from my 10 sentences which gained me a vocabulary of some 30-40+ words, I learned also...
*Directions: Left / Right / Straight / Back as well as North, East, West etc. ( +10 words)
*Whilst at home I learned some useful furniture, etc. such as chair, table, window (+10 words)
*I learned to count to 100 in french, counting and paying in french each time where applicable ( + 100 words)
*Another useful thing is to watch the "Top 3" movies in that particular language/country, not only testing your limited understanding but getting a foothold in the culture
*Wikipedia is also a useful tool (mind the POVs and incorrect information) to gain a general understanding of the country you will be communicating in...
Finally equipped with the basisc of some 150+ words, 10+ sentences and some general knowledge I went to france and was able to find my way through it without english. Mind you, it took me a resource of some 250+ words in each language to manage a basic conversation in a pub or on a street. But with 150+ words you are getting nearer :)
The same I applied to spanish and managed to gain some good friends for many years to come, whilst my collegues had to stay in hotels, etc. I was welcome in their private homes. The language is the key to any culture, learning it shows respect and appreciation as well as ultimately skill. People will respect you for that.