Wouldn’t you want wakaremasen (not able to understand)?
ETA: Though I guess functionally they’re pretty similar.
When dealing with an emotional girlfriend, just say, “I don’t speak girl.”
(Sorry, I heard that once and have used it since even though I’m female. The thread reminded me of it. :))
Hola, me Ilamo es Brian… Nosotros queremos ir con Ustedes… Uhhhh…
Hey, that was pretty good, except when you said, “Me llamo es Brian,” you don’t need the “es,” just “Me llamo Brian.”
Oh, oh, you speak English.
No, just that first speech and this one explaining it.
You…you’re kidding me, right?
Qué?
The OP wrote Ich spreche nicht Deutsch, which means literally “I don’t speak German.”
psychonaut popped in with Ich spreche kein Deutsch, which is literally “I speak no German,” but is what one uses to say “I don’t speak German.”
jjimm added Ich kann nicht Deutsch sprechen, which is “I can’t speak German,” and I assume he maybe misread kein for kann?
Then Acsenray (when did you cap the A, btw?) adds Ich kann Deutsche, which means “I can German,” when I assume you meant either Ich kenne Deutsch or Ich kenn’ Deutsch, which is “I know German.”
FTR, psychonaut has the right of it, but if you’re married to nicht then say Ich spreche Deutsch nicht, which is also literally “I don’t speak German,” but with a word order that sounds more natural to me.
Fulfulde (West Africa): Mi nonnota Fulfulde. (me non-NAH-ta full-FULL-day).
Translates as “I am not/will not be hearing Fulfulde.”
“Wakaremasen”, in the sense of not being able to understand is not used. If you don’t get it, it’s always “wakarimasen”, the potential form is not needed. (The root verb “wakaru” also means “to split”, and “wakaremasen” can be used to mean “(I) can’t split it”.)
Tacking “watashi wa” before “nihongo dekimasen” is a good way to emphasize that you don’t speak the language; fluent speakers never speak that way: the first person is always assumed if no context is given.
Hebrew: “Ani lo midaber Ivrit” or “Ani lo yode’a Ivrit”. The first is “I don’t speak Hebrew”; the second, “I don’t know Hebrew”. Both are acceptable.
Pronounced: “ah-NEE low mih-dah-BEAR/yo-DEH-ah eve-REET.”
There is a universal way of saying this that works in every language: when they start talking to you in a language you don’t understand, just shrug your shoulders and look bewildered*. They’ll figure it out.
*If you really want to get the point across, wear a hat with a picture of the flag of your country of origin and point to that while shrugging.
Thanks, I can speak Japanese decently, but I’m not always sure of nuances. Come to think of it, wouldn’t the negated potential form translate closer to “I am unable to understand” meaning more along the lines of “even if you taught me, I wouldn’t get it”?
It doesn’t even mean that; if you wanted to express an impossibility to understand, you would say something like “rikai dekimasen”. “Wakaru”, by definition, expresses a potentiality, and thus has no potential form. Furthermore, “wakareru” exists as an intransitive verb, and that’s what anyone would hear it as. “Nihongo ga wakaremasen” only really parses as “Japanese doesn’t break up.”
No, he had it right. “Ich kann Deutsch” is a perfectly good idiom for “I can speak German”. “Ich kenne deutsch”, on the other hand, would probably be considered a mistake.
I did it that way deliberately, because of the ambiguity of “y” which can be misunderstood as a vowel. How would you do it?
I sit corrected. Thanks.
A quick stroll down memory lane and a dictionary later, the Latin version should be “Latinum non loquor” (phon.: lahteenoom non lokwor).
Spanish is “(Yo) no hablo español”, though I suppose “no comprendo” would do in a pinch if you repeat it often enough 
In standard (Mandarin) Chinese, the name of the standard (Mandarin) language is “Putonghua,” and means just as you describe. It’s generally the Beijing dialect. In a way, it’s like how we associate newscaster English as being kind of a “common” or standard English.
It’s important to know that it’s a common, standard language because it’s the only really mutually intelligible language in China. There are lots and lots of dialects with different levels of intelligibility with Mandarin, plus a lot of languages that have nothing in common short of Hanzi (e.g., Cantonese).
I suppose there’s the possibility that if you say you don’t speak Mandarin, there’s the possibility that you might speak Shanghaiese or Nanjingese or some other Chinese dialect. In any case, the word “Putonghua” is what my language teacher is teaching me to say.
And this is the difference between Pinyin and other Romanization systems. Not writing “Zhongguo” (even without the diacritics) looks strange to me.
And because I’m a bad student, I can’t really remember what I was taught about the spoken language versus the language in general. Instead of (English) “yingwen” (the English language) it’s something like “yingru” (spoken English).
I can read a few different languages, and I can speak and understand about three others, and one of those really quite well, but Chinese isn’t one of them. This means that in the moment of truth, I freeze (uncharacteristically) and say “ting bu dong” as my way of saying, “I’m very sorry mate, but I’m unable to understand a single thing that you’re telling me in Chinese.” 
Although it is not correct to say that *kann *is a form of the verb kennen, right? *Kann *is just like its English counterpart can, an auxiliary verb. That said, I believe that kann/can and kennen/know (and other similar words such as the Scottish ken) are all etymologically related.
Ich kann Deutsch is good, but that’s not a form of kennen being used. It’s a form of können. Literally, it’s “I can German”. Can you German? Yes, I can.
ETA: Ximenean has this right, including the etymological relationship.
I can’t resist posting a classic Kids in the Hall sketch here.
You might as well just look on Babelfish or Google translate for your answers. If they’re slightly wrong, as many of the examples were, it doesn’t matter - in fact, it proves that you really don’t speak the language.
It’s tricky. The Cyrillic is Я не говорю по-русски, but there’s no real way to translate не phonetically. English speakers don’t make that sound. I always see it as nee (or Knee), but that doesn’t convey the Y sound. Russian e is pronounced like yeh.
Closest I can think of would be:
Yah n-yeh gah-var-you pah roose-key
OR
Ja n-yeh gah-var-ju pah roose-key
(pronounce roose like loose)