No Yahoo traffic on non-English sites

Any pointers please?

[Web_Savvy]

We have several sites with English language content and several more which are written entirely in other languages.

All are coded and structured in almost the same way (with completely different, country-specific content), all are excessively optimised for the human visitors and none are particularly optimised for spiders.

While all the English language sites get decent traffic from Yahoo (ranging from about 20% to 45% of total), none of the non-English sites get even 10% of total traffic via Yahoo.

We're at a loss to understand why this is happening. Any ideas, please?