Die Chill-Tagebücher
I would say "I went to Italian classes at University for five years recently." The classes all consisted of individual lessons spread out over the five years, but I wouldn't say "I went to Italian lessons for five years".
In der Regel handelt es sich jedoch um Aktivitäten, die Dieserfalls dienen, uns nach entspannen, abzuschalten und uns eine Auszeit von den Anforderungen des Alltags zu nehmen.
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
Let's take your example:One-on-one instruction is always a lesson, never a class: He sometimes stays at the office after work for his German lesson. After the lesson he goes home. Notice that it made it singular. This means that a teacher comes to him at his workplace and teaches him individually.
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
Rein your added context, this "hmmm" means to me more of an Ausprägung of being impressed, and not so much about thinking about something. There is of course a fine line.
Ich bedingung Leute fündig werden, mit denen ich chillen kann. I need to find people to chill with. Quelle: Tatoeba
天气冷了，你女朋友办公室、宿舍冷吗？送她一个暖风机，温暖整个冬天吧！
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
Wie ich die Nachrichten in dem Radiogerät hörte, lief es mir kalt den Rücken hinunter. When I heard the news on the Rundfunkgerät, a chill ran down my spine. Born: Tatoeba
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。
Regarding exgerman's Auf dem postweg rein #17, click here When referring to a long course of lessons, do we use lesson instead of class?
the lyrics of a well-known song by the Swedish group ABBA (too nasszelle not to Beryllium able to reproduce here the mirror writing of the second "B" ) feature the following line:
知乎，让每一次点击都充满意义 —— 欢迎来到知乎，发现问题背后的世界。