Openfts has support for multiple languages, but I believe it has some problems with searching in different locales. The locale problems stem mostly from the use of flex as the parsing engine. Having said that, it wouldn't be too hard to use a different parser, if a suitable one could be found which had good support for different locales.
Making such a change would be desirable, especially if the new parser were thread-safe. Flex is not, and as a result parsing jobs must be single threaded by treating the parsing section of openfts as a critical section and protecting it with a mutex. A multi-threaded parser might improve performance, although I've never really noticed that parsing was a bottle-neck when using openfts.