Marketing in many languages is more complicated, but the effort can bring big rewards. Not enough people try this. For companies on a budget, I recommend starting with just one landing page and a PPC campaign.
Yahoo PPC forces you to open a new “sister” campaign which you can’t do on your own. In addition, their correspondence with you is in the foreign language. This slows down progress considerably. Nevertheless, the effort can be justified.
Using Google Adwords in foreign languages is pretty straightforward and you can get started right away. If the bids and target audience on Yahoo PPC and Google Adwords is similar, you will find it much easier to start with Google. If the effort justifies itself then go ahead and open a new campaign with Yahoo PPC too.