I would like do add 坐坐 (zuo4zuo4) which means in german vorbeischauen, kurz anhalten to my vocab list. How does it works if the expression is not a result in the skritter list?

Just enter it into a list. Skritter will tell you that it doesn't exist so far in the database and asks whether your want to add it - yes.
Then it asks whether you want to add as word or as sentence - word.
In the window that opens put in the definition, look that language is selected as German and save.

That's it.

Well this does not work. If I want to add 坐坐 the pinyin will be zuo4zuo5 which I don't want and if I want to add zuo4zuo4 another vocab will be shown. So it semms to be a tricky.

Not sure that 坐坐 (zuo4zuo4) means vorbeischauen, kurz anhalten generally - this is a implied meaning derived from a specific scenario but not the meaning of the word in general surely?

Well I study with gurulu.com for the HSKI and they combine the 150 vocab so that you learn some more vocab. They translate 坐坐 (zuo4zuo4) generally with vorbeischauen, kurz anhalten.

坐坐 (zuo4zuo4) and 坐坐 (zuo4zuo5) are the same word - tone of second syllable is personal/regional preference issue. Repeat of verb 坐 (zuo4) usually is just to soften it - which is often why repeat verbs - e.g. 坐 (zuo4) meaning "sit" can sound like an order, 坐坐 (zuo4zuo4) could be translated as perhaps "please sit" in most scenarios - more of a suggestion. I'd imagine the general translation of 坐坐 is simply sitzen or something same as 坐 (zuo4) - see http://www.handedict.de/en/chinesisch_deutsch.php?e=27045 - this matches skritter translation.

Had a look at gurulu.com "Survival Chinese: HSK 1" dialogue and saw the below on english version - I've put my comments in brackets after it.

Nǐhǎo.
你好
Hello, How are you? {I'd translate as simply Hello}
-
Wǒ hěn hǎo, nǐne?
我很好。你呢？
I am very well, and you? {The translation is fine, but for me that's an unusual response to 你好 - more a response to 你好吗？ really}
-
Wǒ yě hěn hǎo. Nǐ jiào shénme？
我也很好 。你叫什么?
Good. What's your name? {I'd translate as "I'm also very well. What's your name?" which matches the words better}
-
Wǒ jiào Susan, nǐ ne. {why no question mark, like did above? lack of care}
我叫Susan，你呢？
I am called Susan, and you?
-
Wǒ jiào Dawei.
我叫Dawei。
My name is Dawei. {this name is probably 大为 Da4wei2 a transliteration of David often - strange (and unhelpful) haven't done it properly in pinyin and characters}

I'd stick with chinesepod or other big service that has very good translations - and big community to catch errors - although don't know of any in german I'm afraid.

Pentesilea, I support what ricksh is saying. Nevertheless, if you want to keep this meaning in skritter, I propose you enter it as a user specific definition, not as a correction.
Skritter can have only one entry for a given character or word, even if there are more than one pronunciation.
So keep the definition as it is in Skritter and just add a second pronunciation (make a shift-enter after the first definition and then enter your second. Don't tick the box "shared as correction").
But I also have my doubts whether they give you a proper definition for this word, it might be a very "free" translation just in this specific case.

坐坐 is the reduplicated form of the verb 坐, and this form of verb reduplication comes with a tone sandhi. For example, 找找 is zhǎozhao, 跑跑 is pǎopao. The second character is always a neutral tone.

The literal meaning of 坐坐 is “sit for a while”. But more often, it's translated into “to stop by”, “to come round”, or “to visit.”

Thanks for your informative answers. I already had the suspicion that some of their translations in the training sets are relatively free. But for the Preparation for HSK there is just little practice material online.

Have you tried Popup Chinese ( popupchinese.com ) HSK material? I have not, but I know its there. Might be worth a look. Their podcasts are very good.

pts - what's the source of that tone sandhi - not saying it is wrong, think I always agree is how say it, but for e.g. both nciku and yellowbridge have 坐坐 as two fourth tones

Pentesilea - I think HSK lists are not comprehensive enough to justify learning based on the words in them, hence not many resources so closely linked to HSK. You can learn the whole 5000 HSK list words, and you still won't be able to say Germany (or any other country but for China I think) in chinese, but you will be able to say sugarcoated hawthorn. Better to just do dialogues from chinesepod or more popular service, then once know say 95% of a HSK list do tidy-up and learn rest if you want to do HSK test. Plus if, for example, aiming for HSK 4 no special reason to learn all HSK 1 before learn rest of words in HSK lists that apply to you. All the exercises in chinesepod are thus practice for HSK, on basis need to learn beyond those words anyway. Same applies for other services like popupchinese etc. Well, that's my theory anyway!

Searching the web, one can find a lot of articles talking about how to read this kind of 重叠词. The following one from baidu is just one of them. http://wenku.baidu.com/view/89745c442e3f5727a5e9624f.html

Thanks pts - will take a look

I work with fluentu.com for chinese dialogs. For HSK gurulu.com is fine I think. They drill each part by hundreds of sentences. I would love to have a tool which shows me all the possible words which are combination of the characters I choose. Does anybody knows a thing like this?