(traditional) Noto Sans T Chinese
Recently Google have released the new Noto Sans font family that supports wide range of languages including Traditional Chinese in aiming to achieve visual harmonization across all languages. This font is licensed under Apache License 2.0 and can be used for commercial works.
This versatile font family was developed together by Google and Adobe, under the name Noto Sans CJK and Source Han Sans respectively. You can find Adobe’s Source Han Sans Traditional Chinese hosted here at Typekit, SourceForge and Github.
Free for personal and commercial-use.