Well，it is complicated and confusing when speak ‘ I Love You ’ in German.
Here are what you would hear in German and I seached some explaination for that on Internet.
1.Ich liebe dich
2.Ich hab(e) dich lieb
3.Ich hab dich gern
4.Ich mag dich
5.Ich mag dich sehr gern
I don’t think both in English and Chinese would have such a subtle difference, but indeed, German has.
‘Ich liebe dich’ would be the most common word for ‘I love you’, it is used explicitly for girl/boyfriend or the closest family members. it is just a declaration of your love, and emphasize ‘I’
‘Ich hab(e) dich lieb’ is usually used among familar memebers, it implies something like I love you and I can endure you or somthing you have done and experienced. It implies some complicatied emotion or relationships between familar members. In English, it is more like “you have my always love/bless”, emphasize ‘You’
‘Ich hab dich gern’ is a variant of ‘Ich hab(e) dich lieb’, I think it is more slight in emotion.
‘Ich mag dich’ is the version of ‘I like you’, it is the slight version of ‘love’, not intimate as ‘love’, all friends can say ‘mag’ without much affectionate effect.
“Ich mag dich sehr gern” basically it means ‘I like you very much’ still, it is not much emotional, among friends is commonly used.
In English, there are some slang to express more complicated emotion for ‘love/like’ such as ‘I dig you’, but they are not as formal as German do.
In Chinese traditional culture, People are conservative to talk about ‘love’ so the expression is simple just
我爱你 (I love you)， and the slighter version of 我喜欢你(I like you), in most typical Chinese family ,you barely hear such kind of words, so mostly it is used among friend or lovers. BUT in China,even ‘I like you’, is not as in the same context as in English， it also implies some kind of intimacy between each other. So Don’t use it as well, otherwise, others may misunderstand you.
Then, if you want to express the meaning of ‘I like you’ to a good friend from China, a compliment is a good choice, such as ‘ you look great’(你好棒), ‘you are great（你好棒）’ ‘you are awesome（你太棒了)’
After I wrote this, I also find it is kind of wired or such a significant difference between cultures.