How to detect the language in a TextBox

[harvinders]

It is possible to input text in multiple languages in a TextBox. However, it is not clear how could we retrieve that information (language used). The example below shows a TextBox with 4 different languages.

Though very unlikely in real world, it is however possible for people to mix english and another language. How do we figure out which language is used? There doesn't seems be an API to figure that out, or am I missing something?

I am using QuestPdf to create a pdf with the text in the TextBox and QuestPdf requires us to specify the font used, if I can't know the languages that are used in TextBox, I can't specify the font to use.