A reasonable idea, and considering the Army are more likely to be face to face with non-english language people on a daily basis while in theatre out of the three services while out patrolling or dealing with the local pop's reps. It could solve a lot of on the ground problems and goes a long way in hearts and minds.
But having a group of linguists within a battalion is useless for that purpose if they don't speak the right language and they don't deploy on all the patrols.
If a battalion is needed to go to Poland, will the army care if the company commanders speak Russian, Farsi, German & Arabic? Do you think those officers will get binned and that the army will scrape through the army looking for Polish speaking infantry captains to dump into that battalion? I doubt it.
As I understand it, the purpose of having a language skill is so that you can be deployed to embassies, international headquarters, multinational forces or be deployed as a liaison officer (so whilst we might not scrape up four polish speaking captains for the above deployment, we might want a polish speaking Maj. or Lt.Col. attached to HQ Coy. to play nice with the host country).