中文翻译成英文，不要用转换器！

I stand on your side forever. Cheer up!

Cheer up,在特定环境下,与come on同意,都表"加油!"

或说, I back up you forever.Cheer up!

偏向精神上的支持多用on one's side.
否则多用support,行为及物质上的. 当然精神上的也可用.口语不多见.

I support you forever. Cheer up!(或Come on!)

另这种一定要用现在时态. 不用将来时态,因为说的时候,已经是在支持了.

I'll always support you.Add oil!!(add oil说法已经被许多专家和外国人接受,相信不久大家都明白汉语"加油"的意思)

I will support you forever! Go! Go for it!

I'm always back up you!
Come on!

i will be for you forever. Jiayou!

I am always with you,cheer up!