Most, if not all, Japanese games will just run a bit slower on your PAL MSX, but apart from that will work just fine. You can even manually set your MSX to NTSC mode, but inserting cartridges while your MSX is on is not exactly a clever idea. (Although most visitors will probably have to admit they all did it at some point in time ;P)
As for Japanese texts: as long as Japanese game/software don't use the KANJI ROM (and most don't, as the KANJI ROM became a standard only in 1988 with the introduction of the MSX2+) the Japanese text will work on European MSX computers as well. If you want it to work in all cases, you should consider obtaining a 2+ or turboR
