I have a feeling the point wasn't clear enough above. Let me sum up:
There are three primary interfaces for mice: Serial (RS-232), PS/2, and USB. (Also bus mice and some other less popular interfaces, but let's ignore them for now.) These three protocols are entirely different, and have different physical connectors (obviously). Some passive adapters exist to change the plug and wiring, but it does not translate the protocol at all. Those passive adapters are intended to be used with mice that have a controller chip inside that natively supports multiple protocols, and can determine which is being used by the signalling levels or how the system probes for a connected device.
During the transition from serial mice to PS/2, it was common to buy a mouse with either plug on the end of the cable, and it would ship with a passive adapter to connect to the other. The mouse itself would automatically adapt to whatever interface it was plugged in to, possibly via the adapter. Same happened with the transition from PS/2 to USB.
So, there do exist a lot of multi-lingual mice, but you have to know for sure your model can, and which protocols it supports. If it's a new mouse -- like, XP and up -- it probably doesn't support anything but USB, since by that time, USB had pretty thoroughly taken over from PS/2. Also, not all adapters are wired up the same way, since this was never a standard. There were probably some common arrangements (as there tend to be), but any manufacturer could design their adapter to do whatever they chose to do.
The solution is to have an active circuit, which natively speaks both protocols, and translates accordingly. There are community projects (linked above) and commercial products that do this, although they are not as common as you would think. The exception is anything-to-USB. You can get a USB-to-serial adapter or a USB-to-PS/2 adapter pretty easily, but this only allows newer USB-only computers to use legacy serial and PS/2 peripherals.
In comparison, PS/2 (computer) to USB (peripheral) is a relatively complicated problem to solve, requiring a micrcontroller with a full USB Host stack. Even then, it's not a guaranteed success since USB can and does implement standard (driver-less) device classes, but can also require specific drivers to support functionality beyond the absolute basics. (This is why you might see a commercial adapter say something like "does not support wireless KB/mouse.")
Serial (computer) to PS/2 (mouse) is more straight-forward, but there aren't a lot of products on the market to do it. Nobody has cared for a long time about serial mice, except for communities like this, and so communities like this are where you'll find home-brew solutions.
Hope that helps.