since as far as I know, jap version have different pokemon in-game in comparison with the occidental version
This is true only for blue-jp version. If you played red-usa, then you had the same pokemon availability as red-jp. Let me recall the timeline of changes.
1996 - Red and green versions are released in Japan.
1997 - Blue version is released in Japan as a special mail-in order product. It is the first "third version" of a pokemon game. The game has redrawn front sprites for pokemon, a unique super gameboy border, updated tilesets, bugfixes & engine improvements, and a revised cerulean cave dungeon. Pokemon availability through casino prizes, npc trades, and wild encounters is also modified.
1998 - The year of the USA releases of red and blue versions. But these are not translations of red-jp and green. The localization team took the code base from the Japanese release of blue and split that into red-usa and blue-usa. Their red-usa altered the code to replicate the pokemon availability of red-jp (along with restoring the original intro and super gameboy border). Their blue-usa version altered the code to replicate the pokemon availability of green. The localization team essentially created their own rom hacks and released them to the west.
Also in 1998 - Pokemon Yellow releases in Japan. It is effectively a "fourth version" and features new pokemon front sprites, another overhaul to the tilesets, following pikachu, easter eggs from the anime, harder bosses, an even more updated engine with stereo sound, new pokemon availability, and a second revision to cerulean cave.
1999 - Pokemon Yellow is released in the USA and becomes their "third version". The only change it has from its Japanese release is that its built-in super gameboy palettes are now adapted and converted for display on a gameboy color screen.
The west has never seen a release that replicates the pokemon availability of blue-jp.
Now as for finding a translation, Moriyafaith's jp rom hack project does a faithful replication of blue-jp since only some data tables have to change. If you want it with all kinks and glitches worked out of Gen 1, then you are going to want the latest beta patch of my own
Shin Pokemon Blue-JP Lite.
