What languages did the church in Corinth understand?
The church in Corinth primarily understood Greek. Most of the congregation was able to understand Greek, but some could not; those individuals perhaps understood only Hebrew or Aramaic. Thus the languages they understood were Greek, Hebrew, and Aramaic, with Greek as the predominant language.
Les explains that Paul knew what he was talking about regarding languages, comparing it to missionaries today who must attend language school for four or five years before going to the field. He notes that in the Corinthian congregation, most could understand Greek, but some could not; those people only understood perhaps Hebrew or Aramaic. Paul desired that they could all teach and preach in a language everyone understood so the church could hear the Word, since they could not go home and read it.