I can remove any subtitles but that's because the UOP was disabled as part of the mod.
Usually if you can remove subs via the menu you can just use your SUB key on the remote to switch them off although this is not always the case . Disney titles will often need to return to the menu. Speaking of Disney , the disabled UOP also means you can change the ANGLE on the fly so when Disney present alternate foreign language opening titles usually only accessible by selecting the relevant audio track you can switch between them as the film runs.
Back to subtitles and the Spanish Hammer Horror dvd's had subs that were removeable but they were tricky as you had to select your audio track , then start the film then return to the menu to select no subs then restart the film . If you tried to do it all at once the subs would appear.
If you buy foreign discs regularly I can't recommend a UOP disabled player highly enough but I only know one company in the UK that offers that mod so I don't know what the US options are other than the programs you can buy to use for computer playback where removing subs should be easy