Three days ago I knew met a japanese tourist in Barcelona

I was waiting to for my wife outdoor outside of the theater. She went with her friend Noemí to enjoy a musical representation like a Broadway show.
I was walking for there, and then a Japanese come me came closer to me (<em>or</em> a Japanese man approached me) and he asked if he could use my cellular for calling to call a Spanish number, so because with his phone he could not do it. I left gave him my phone and he rang a telephone number and asked by for Mónica, all this in English. But Mónica hunged hung up the phone because she did not understand to the Japanese tourist. I cought took my phone and I rang again. Mónica, I said. Here there is a Japanese man who wants to talk with you, I followed saying. Mónica said to me, she did not understand to the boy, because she did not speak English. I translated the conversation between both of them.
Finally I helped them to meet and I think they went to Andorra in the Monica’s car.
I’m happy for helping them (<em>or</em> I was happy to help them).

See you later.

Good story! My corrections are in red and my suggestions to sound more natural are in blue/grey.

Mónica said me, did not understand to the boy - You could say this either:

Mónica said to me that she did not understand the boy

Mónica told me that she did not understand the boy

Three days ago I knew a japanese tourist in Barcelona

I was waiting to my wife outside the theatre. She went with her friend Noemí to enjoy of a music representation like Broadway.
I was walking just there, and then a japanese come to me, and he asked if he could use my mobile phone for calling to spanish number, so with his phone could not do it. I left him my phone, he called a telephone number and asked by Mónica, everything in english. But Mónica hunged (hanged or hung) the phone because she did not understand to the japanese tourist. I caught my phone and I called again. Mónica, I said. There is a japanese who wants to talk with you here, I said. Mónica tell me She hadn't understood to the boy, because she did not speak english. I translated the conversation between them.
Finally, I helped them to meet and I think they went to Andorra in the Monica’s car.
I’m happy to help them.

See you later.