if they are japanese then they will be japanese, but some games are easy enough to get around since they have just enough English to deem playable. The US PSP games are out soon so maybe you should get one of them now.
so far i have got:
NFSU Rivals JAP, thats a really great game and the JAP text can be off-putting but you tend to get used to navigating the menu and stuff,
Ridge Racers, this is probs the best of all the games ive played so far, very addictive and despite being japanese it is very very easy to get around the menus and stuff.
Metal Gear Acid, this is 'too japanese' for its own good, but after a few hours or so of trying to get used to it, the game can be pretty addictive and cool. The plot is a total mystery for me, so it is better to try and wait out for the US version of this to be honest.
these are the only games ive tried so far, my dad got the Everybodys Golf game not had a chance to play it personally, but he says its also 'too japanese' to deem playable.
so, if i was you i'd either wait for the US games or get Ridge Racers, since it is the best game so far, and since the US version will be out soon i can imagine the price of the JAP one might go down (or ppl will auction them off cheaper on eBay)
hope this helped