One of the details that gets lost in the transition of manga-to-anime for Fullmetal Alchemist, is the overt presence of foreign language. For example, the Xingese characters actually regularly speak Xingese amongst each other. While they aren’t the only example of foreign language being spoken, they are the most prominent.
In the anime, every character no matter what race or what country they are from, speaks the same language as a translation convention. The only real hints that there are other languages present are very minor, like the fact that Ling wrote his message to Lan Fan completely in Kanji and that no one outside of them could read it.
However, the manga has an interesting convention to denote that foreign language is being spoken, by giving every foreign language speech bubbles that are horizontal instead of vertical. This is lost slightly even when the manga gets translated because in Japanese, the vertical speech bubbles also have vertically typeset dialogue which help better distinguish the languages. Nonetheless, the speech bubble shapes are very distinct.
When Ling talks to Ed, his speech bubbles are all vertical
As are Lan Fan’s
But look at Fu’s thought bubbles here and compare them to Paninya and Al’s vertical bubbles. They’re horizontal! Fu is shown to be thinking in his native tongue!
Conversations that we heard all in one language in the anime, were supposed to be in Xingese.
Like Ling, Lan Fan, and Fu on the roof.
And Ling speaking with Mei at the end of the final battle.
Its just one of those really neat details Arakawa uses that makes FMA’s world just a bit richer in the manga than what we see in the anime version of the series.