Good question. I just installed the Spanish version of Office 2010 - big mistake as I now have the same problem as you. As far as I can see the keyboard shortcuts go with the UI (ribbon, menus) language. If you want English shortcuts you must install the English UI. The only way for you now to get the English UI is to purchase an English language pack.
If you (theoretically) start from zero, you have three options if you want to use English shortcuts:
- Purchase Office in English. You get the UI in English and proofing tools (spellchecker etc) for English, French and Spanish. If that's all you need, problem solved!
- Purchase Office in English and then purchase a language pack for your language.
- Purchase Office in your language and then purchase an English language pack.
Both options 2 and 3 will give you the ability to set the UI into English, and use the proofing tools for various other languages. See the proofing tools you get with a language. You are only able to set the UI into the primary language of the Office edition or language packs you have.
Update: As of Office 2016, language packs are now free. You can download them from the Microsoft site.