If you were to say:
If each person learns one of the languages, then the languages will be protected
would the 'aprender' be conjugated in the subjunctive?
Si cada persona aprenda uno de las lenguas, entonces se protegerán las lenguas
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In this type of conditional structure you can use several patterns (and you can't mix them). The patterns are not that different from those of English, except of course in English the present subjunctive is not distinct from the past indicative.
So, using you example as the model (and translating a bit more naturally):
The first example (using the indicative) is a general conditional statement. It may refer either to a condition in the actual present or be a timeless statement. It implies that the condition might be fulfilled at any time. If you do X, then Y will happen.
The second example (using the imperfect subjunctive) is a hypothetical statement. There's not that big a difference with the first example but there's a sense that things are not that easy; the condition might very well not be fulfilled. If you did X (but maybe you don't, who knows?) then Y would happen.
The third example is rather different (and not what you asked for, but I'm including it for completeness' sake). It's a counterfactual hypothetical statement, that is, a hypothesis about an outcome that didn't take place. If you had done X (but obviously you didn't...) then Y would have happened.
There's another possible pattern that uses the future subjunctive, but the future subjunctive has fallen into disuse (you'll only find it in legal documents, mostly).