Especially for Chinese, there is a lot of work on joint word segmentation and POS tagging, e.g., (Zhang and Clark, 2008;Sun, 2011;Hatori et al., 2012;Zheng et al., 2013;Kong et al., 2015;Cai and Zhao, 2016;Chen et al., 2017;Shao et al., 2017), of which some use CRFs to predict one POS tag per character.
this is hard to transfer to languages like English and Vietnamese where single characters are less informative and tokens are much longer, resulting in a larger combinatory label space.