One thing that I hear time and again by even my more advanced students are sentences like: “Ich werde dich besuchen, wann ich wieder in Irland bin” or “Wenn ich 10 Jahre alt war….”.
The English word “when” has three different translations in German.
The most well known is wann.
“Wann” is only ever used in questions?
Wann kommst Du mich wieder besuchen? (When will you visit me again?)
Wenn of course looks and sounds very similar and can therefore easily be mixed up, but is used in sentences (not questions) for future events or when talking about regular occurences:
Wenn ich nach Dublin fahre, werde ich dich auch besuchen. (When I travel to Dublin I will also visit you.)
Immer wenn ich Kopfschmerzen habe, nehme ich eine Tablette. (Whenever I have a headache I take a tablet.)
Last but not least we have als which again is used in sentences when discussing past events such as:
Als ich 10 Jahre alt war, habe ich erstmals in einem Flugzeug gesessen. (When I was 10 years old I sat in a plane for the very first time.)
*Wenn in sentences discussing the future or regular occurences
*Als in sentences discussing the past
