Input method engines

Chinese

• fcitx5-chinese-addons. It includes most common input methods used by Simplified Chinese including engines for Pinyin and Table (Wubi, etc).
• fcitx5-table-extra. Additional Chinese Table
• fcitx5-chewing. Chewing engine based on libchewing.
• fcitx5-zhuyin. Zhuyin input method engine based on libzhuyin.

Japanese

• fcitx5-anthy
• fcitx5-kkc
• fcitx5-mozc
• fcitx5-skk

Korean

• fcitx5-hangul

Vietnamese

• fcitx5-unikey

Thai

• fcitx5-libthai

Sinhala

• fcitx5-sayura

Multilingual (If it is not listed above, this is probably what you need)

• fcitx5-m17n
• Builtin keyboard layout based engine.