Indeed, language teachers have not been trained to teach content subjects, and may be questioned about their credibility in CBI courses. From my perspective, I would say that language teachers can ask for assistance from content teachers. Additionally, language teachers can choose a content subject that they are familiar with to instruct. Do not try to teach all subject matters, that is, language teachers should start small. Finally, language teachers can attend professional development workshops to let themselves have second, third, or even fourth profession.
Another problem associated with CBI is that language teachers are too concerned with content area teaching and neglect teaching related language skills. Language teachers seem to forget the main purpose of CBI is to enhance language development though content areas rather than content learning per se. If language components are missing, it can not be called CBI. The language learning aspect should have equal priority with the content learning facet in CBI (Cristopher, 1996).