My personal opinion on this would be, that if a person makes a mission only on his native language and doesn't bother to make it more universal by translating to english, it's his shame.
I think OFPEC should continue taking mission build with other languages, but including a bold text in the readme which states the language in question.
For example I know a great many mission build with the FDF mod and finnish language, which just make the finns go crazy because they can enjoy the mission on their own native language. If such would be submitted to OFPEC, it should state that it's in finnish language only and from that some people would know not to even bother downloading it
I agree that there should be an english version of a mission always included, or a separate briefing in english and/or english in the stringtable and/or a starting parameter to select language, but I don't agree that missions without english should be ruled out.