i will join you

По-моему, для I'm going to join you нужен комментарий, так как во многих ситуациях это может звучать неуместно. 🤔

I’M GOING TO JOIN YOU is a definite plan on the part of the speaker - they intend to do this: [wife] Honey, we won’t be home when you get here. Annie has her piano recital tonight and... [husband] I know - I’m going to join you. However, WILL has a more tentative effect. It implies that the speaker is offering to do something, or suggesting doing something tentatively as long as the listener is ok with it: [woman to neighbor1] You know, there’s a free concert in the park today at 6. We’re taking the kids. [neighbor2] Oh, how fun. We’ll join you. (<— here neighbor1 can say Great! -or- Hmmm, we’re taking the dog and you know how you’re kids are afraid of him...)

👍 I meant that without any comment in Russian, the translations like "I'm going to join you" might confuse people who ask questions.
So Uly did the work for Elena. (Aren't Lena's comments in brackets self-explanatory?).