Research has found a positive correlation between the English proficiency, teaching self-efficacy and professional development (PD) of English-as-a-Foreign-Language teachers who are L2 speakers of English. Yet, there is scant research on these variables for teachers of other languages teaching in English-speaking countries. This mixed-methods study investigated the connections between perceived English proficiency, self-efficacy in applying professional standards, and PD of secondary-school Chinese language teachers in the State of North Carolina. Quantitative results identified participants' perceived English proficiency as a significant predictor of self-efficacy. A significant negative correlation was found between participants' perceived English proficiency and PD benefits. Qualitative results indicate that participants' self-efficacy and perceptions of the benefits and support of PD were positively impacted by affirmation and emotional support, whereas cultural barriers and lack of PD self-initiation had adverse effects. Analyses of the integrated findings also address the study's implications for teacher educators and researchers.