*Not a teacher
They may be similar or they may be different.
Similar: Eg Paul spoke to Fred yesterday; Paul talked to Fred yesterday. In both cases, Paul had a word with Fred, no more related. That's clear.
Different:
=> Eg Paul can speak English; Paul can talk English. Here, speak implies a capacity, a can-do in a specific language while talk does not.
=> Eg Paul is speaking about the weather; Paul is talking about the weather. In that case, we do not care about the capacity of speaking a language. The matter is the weather, the discussion about the weather. So Paul is talking about English would be fine.