Maximizing English as a foreign language (EFL) students' use of their second language (L2), minimizing native language (L1) can help them to develop L2 proficiency. In the monolingual approach, the exclusion of L1 is preferred. However, students' use of their first language (L1) in code-switching or translanguaging can be advantageous. This study examines the effects of L1 use on six advanced EFL speakers' willingness to communicate (WTC) during L2 conversations to evaluate the potential advantages of L1 use in an EFL context. Participants were recruited for the study, presented short speeches, and underwent interviews. L2 (English) use was required, but selective use of L1 (Japanese) was allowed. Thus, code-switching and translanguaging were expected. All participant utterances were recorded, transcribed, and analyzed. Participants self-assessed their WTC for each utterance; a stimulated recall interview was used to collect qualitative data. In general, the result showed that the participants' WTC was somewhat lower when talking in their L1 versus their L2. However, the findings also revealed the complex nature of WTC underlying the use of L1 in the form of code-switching or translanguaging, implying that intentional selective use of L1 can be a positive, effective move in L2 conversations.