Tricky-Loops wrote:So, is it wrong to say: "I'm (still) learning English since more than 25 years"? It means even now I'm learning English, after 25 years...
The second form is correct - "even after 25 years, I'm still learning English".
The difference between "since" and "for" in English is that it's "since
a specific point in time" and "for
a period of time". Because "25 years" is a period of time, you use "for". If you were to say when you started learning English, you'd use "since". For example, "I have been learning English continually since I first started 25 years ago" (where "when you first started" constitutes a specific point in time).
Some languages don't make this distinction, and you use the same word for both. So "seit" in German is either "since" or "for" depending on context. You could however think of the difference between "seit" and "seitdem". "Seitdem" means "since a specific point in time". You wouldn't say "Ich lerne seitdem 25 Jahre English" to mean you have been learning English for 25 years (seit 25 Jahren) - you'd need a specific point of reference for the "seitdem" (possibly in the previous sentence for it to work, as with "since then" in English).
Does that make it any clearer?