Anda anak keberapa.which might be translated as "Among your siblings, which number are you?" Note how difficult it is to ask this question in English.
Similarly, in Chinese, you can ask:
你 在 家 中 排 行 第几My dictionary glosses 排行 as "one's seniority among brothers and sisters", which is a good explanation even if it is rather clumsy in English.
ni zai jia-zhong paihang di-ji
you at house-in rank which-number
Why does English lack a word for this? The first thing to note is that seniority among brothers and sisters is less important in the English-speaking world than in East Asian societies. For example, Both Malay and Chinese differentiate older and younger brother (Malay: abang/adik; Chinese: 哥哥/弟弟) while English does not. So it is not entirely surprising that English does not have a word for one's family ranking.
However, there is a wider issue here, something that has been discussed by Arnold Zwicky in his blog (here): you can state "Barack Obama is the 44th President of the United States", but how do you ask a question of this? "Which numbered president of the United States is Barack Obama?" is not grammatical.
It seems that English lacks an expression for asking "which number". Some people have suggested manyeth, so you might ask "Which manyeth president is Barack Obama?", but this has not caught on.
We usually say that, even if a language does not have a word for something, one can almost always express the concept by some other means. But it really does seem that English has no easy way to ask this question.
Try another example: "It is now the eleventh month of the year." Now try and make that into a question. "Which month of the year is it now?" probably gives you the answer "November", not "The eleventh".
