Obviously some tasks require an MA or PhD, but others require simply a modest gift or interest in language and a couple of courses. At Biola University we offer an MA in Applied Linguistics, but we also have students who are taking a few courses, or getting a minor. We're happy to correspond with you about what training you need to fit in to where God may be calling you. A big piece of successfully communicating the Gospel across cultures is learning the language and culture of the people you're talking to. And many missionaries get stuck at this point.
New workers can feel as if they'll never be able to communicate.
Veteran missionaries can be discouraged over lack of progress in spite of time devoted to language learning. But this task can be facilitated by an applied linguist. Many mission agencies have opportunities for language supervisors, or language facilitators, or language consultants. These are people who have proven themselves to be reasonably good learners who are now able pass on language learning support to fellow missionaries. They provide workshops, personalized language guidelines, reasonable structure, accountability, and assessment of progress.