I was wondering how 嘛 is used in this sentence. I think the sentence could be translated as something like "Taiwan only makes low-cost movies about the humanities."?
嘛 has 2 functions.
The first translates as showing something's obvious, much like an "of course" would on the end of sentences in English. An example would be 「你的妹妹很漂亮嘛」if you're taking it as obvious their little sister is pretty (I assume you're using 繁字體). Clearly not the case here, as your example is in the middle of a sentence.
The second function is to signal a topic for emphasis. For example
大熊貓嘛，孩子們都很喜歓。Pandas ah, children all like them"
嘛 is used to provide emphasis. In this case, "台灣都嘛" emphasizes that "As for Taiwan, it makes nothing but low cost movies about the humanities". It's not a perfect translation, but as with all particles, finding an English equivalent isn't always easy, or possible. If you know any Japanese, the particle は can be used for similar effect in many sentences.
Most importantly, 嘛 is emphasizing 台灣都. It marks it out as a topic, and is a small break in the sentence, like a comma in English. You could take your example sentence as
which we can take in English as along the lines of "Taiwan, it just makes low cost humanities movies" or maybe better "Ah, Taiwan, it just makes low cost humanities movies"
i try my best to the 嘛 meaning. it is actually a combination of little complication. i try to segregate them for you. but when in use, it should somehow combine all those factor.
there are a few situations: 1) a situation where out come is resulted from common knowledge. similar to english 'too', 'also', plus some emotional biased sense, emphasized or decimated level of magnitude in term of conversation.
example: WU:"my sister is pretty" -- 我姐姐很漂亮。
AMABO:"my sister is also very pretty too. -- 我姐姐嘛很漂亮。
WU:" google is a big company" -- 谷歌是一间大公司。
AMABO：" intel is also a very big company, too." --英特尔嘛也是一间很大的公司。
(hidden emotion, can be, your item is very good, but my item is also as good or better. or your item is bad, but my item is also as bad or worse.)
2) it derived meaning to similarity, or comparatively to, or like, to some assumed common known sense.
++我妈妈嘛是女的。 --my mother is also woman.（hidden: which is similar to yours and maybe others)
++他嘛脾气不好。 -- he is also a bad tempered guy. (hidden: which compare to know body having bad tempered)
so 台灣都嘛是做小成本人文電影 is in this category. -- taiwan is also making low cost movies。 （ hidden common sense: as compare to japan making low cost blue movie.）
3) a begging words to please to try something as a result of togetherness. -- :wanna meal? ++ 吃饭吗？ xx :no thanks. ++ 不吃。 -- : come'on, lets do it. ++ 吃嘛。。。 xx ： ok. ++ 好吧。
( as a result, they do meal together.)
xx : 这个我不会做。。。 --: i dunno how to do this. ++ : 再试一下嘛。 --: try again please ~~~. ( hidden: beg to try as myself or other people also trying as in situation 2 for common knowledge)
-- 吃一下嘛。++ lets try to taste of the food. (hidden: no harm to try, so please try.)
I suspect this may be an example of "Taiwan style Mandarin" 台灣國語.
In the Minnan dialect, 嘛是 = 也是 (教育部臺灣閩南語常用詞辭典); this is also used in an emphatic form 攏嘛是 to mean "without exception", where 攏 = all (都). Put into Mandarin, it's equivalent to phrases like 都是這樣, or 專門做這種事
Rather than use 攏 long to write this Minnan expression however, some people write 都嘛是, using the Mandarin equivalent of 攏. In effect, it combines a character for a Mandarin particle with a character for a Minnan particle to form a phrase that, if read, would be read in the Minnan dialect.
This sort of mixing of Mandarin and Minnan characters is now fairly common in Taiwan. Look up 都嘛是 and see what you get, it's almost all from or about Taiwan. (Some seems to be from Fujian, so some Minnan speakers there may have adopted this form as well)