Suppose that you will give a talk and in your audience there will be only a person which does not speak your mother tongue. Let us call him John.
Neither your mother tongue nor the mother tongue of John is English. However, you can say some words in English and John can understand it.
As you are not comfortable in speak in English, you will give your talk in your mother tongue.
What should you say for John in order to apologize for not speaking English? I'd like examples of some possible sentences because I'm not sure I can construct a grammatically correct one. I'd like also that the sentence explain the reason given in last paragraph.