Other Languages in UTAU
Despite being a program built for singing in Japanese, many users have overcome this and have successfully made voicebanks for use with other lanugages such as English, Chinese, etc. Keep in mind however, that experience with UTAU is generally needed when making or using voicebanks in languages other than Japanese.
utau.us only catalogs a few voicebanks/recording lists for other languages due to how many there are\so please don't hesitate to search around for the one that you're looking for.
English
Arguably the language with the most recources for UTAU, despite being one of the harder languages to synthesize singing in.
ก VCCV English by Cz
ก VCV English by SRS
ก Arpasing by Kanru Hua (website by KLAD)
Other Languages
These lists/voicebanks do not have a specifice page on utau.us with explanations on how to use, oto, or record them, but do have links to where they can be downloaded.
ก CVVChinese by Risku
ก Syo Chinese by Syo/Big Hands
ก Wang Fangmei Chinese by Natadekoko
ก CV Korean by kangdanim
ก VCV and CVVC Korean by Syeon
ก VCCV Korean by E_via
ก Rentan Korean by bungxin
ก CVVC Spanish by Teren000
ก VCCV Spanish by Aku P
ก CVVC Brazilian Portugese by Leo R