I'm sure it would be an interesting game to translate, but as goldenband said, if nobody's yet pulled it off, there could be a reason. I do find it amusing that YouTube commenters are giving precise locations for text in the ROM, yet aren't doing anything about it.
So anyway, I've opened up my hex editor of choice and looked inside for ASCII text, and there is plenty in both ROMs, so I'll tell you what I can see.
First, X itself.
$3413 - "TIMER EXPIRED"
$3475 - "BONUS.10 X TIMER.GET READY.GO GO GO"
$3668 - "SHIELD DESTROYED.NOT DEEP ENOUGH.TUNNEL DESTROYED"
$7CFD - "GAME OVER"
$9228 - a list of objects, though whether it's used in-game or just for debug purposes I don't know (I have never played the game)
$9F95 - "TUNNEL"
$9FD5 - "EXIT.RIGHT.LEFT.EARTH"
$B672 - another list, looks like a shop as it includes items and "BUY.SELL.CANNOT SELL HERE"
$BA34 - "DYLAN...........FRED............BOB.............SUPERMAN........DYLAN" (high scores or something?)
$C2A8 - dialogue for someone selling 'podules'
$DE03 - "ONE CRYSTAL.WILL RESTORE.YOUR SHIELD.TO MAXIMUM.START CANCELS.A CONTINUES. YOU HAVE NO .CRYSTAL TO USE.YOUR FUEL"
$F5A3 - "COUNTDOWN.OBJECT LOCKED.LOCK OFF. OUT OF RANGE .STANDBY OK"
$11B03 - "MISSION .COLLECT . CRYSTALS.DESTROY .RETURN TO BASE"
$126F2 - "NO HELP.AVAILABLE.FOR THIS.MISSION"
$12ACF - big chunk containing "help" bits and mission descriptions (1 to 15)
$16ABB - "This Base Has Run.$1Out Of Supplies..$1Out Of Missiles..$1Out Of Fuel Supplies..$1Out Of Materials" (finally using lower case... actually, the tech demo uses VWF, though I would be surprised if that code remains in the release version)
$16D9F - "NO SHIELD LEFT!"
$16F3A - "POINT REACHED"
$16F93 - "SILO DESTROYED.VIDEO PIC TAKEN.ROD INSERTED.SILO NOW SAFE.$1DAMAGE HIGH"
$16FFC - "FUEL LOW.PAU ##SED"
$17983 - "RADIO LINK"
$17DB2 - text saying "Mission One" up to ten (not 15, like at $12ACF)
$22B69 - credits (interestingly, it lists four people who helped with English support, and finishes with "LUNAR CHASE....WAS.BROUGHT TO.YOU BY[[.....NINTENDO.\ 1991"
$28C94 - random in-game messages
$391F5 - another credits! Byte-for-byte identical to that at $22B69
That was all just scrolling manually through the ROM while looking at the ASCII text. I'm sure I used a program which can look for potential strings (say, by finding whenever three ASCII characters are used in sequence, for example) but I can't find it. If anyone knows of such a program, that'd be great (in general, not just here).
I won't list everything in the tech demo, because it's mostly the same, though under different offsets. There are differences, words changed here and there, but nothing major. The big thing that's NOT in the final release is the intro, located at $17BD1. Also, it only includes everything up to "NO HELP.AVAILABLE.FOR THIS.MISSION", plus the intro I just mentioned. So nothing from after that in the released ROM is in the tech demo - not surprising since it was a demo.
Whew, that drew me in more than I thought it would. If I didn't know any better, I'd say the ENTIRE game text is in there. Quite astonishing that it's just sitting in the ROM, alongside the Japanese, and it's still only a 2MBit cart. Not gonna lie, I'm interested now.