You don't say if you're on a PC or a Mac but, in either event, you must have the necessary font loaded into your operating system.
What language are you trying to type in?
Welcome to the forum.
Along with the language, please let us know the exact font that you are attempting to use. Some will just not display in PrE's Titler. In those cases, one needs to find another similar font, and use that.
I have seen this with several Asian fonts, plus the Roman Isabelle and Isabella (from several foundaries). A substitution has always fixed things. Adobe programs, in general, are sensitive to fonts. Illustrator, and Photoshop are strict, and Titler is even more strict. The font must be properly written, and any corruption will never work - often even crashing the program. Often, one gets a false sense of security, if a font works in, say Word, but not in an Adobe program - it is the font, and another needs to be substituted.
If this is what you are getting:
then you have chosen a font that PrE's Titler cannot display properly. This was a Kozuka font (free version).
Also, many Multi-national fonts will not display properly, and will default their display to Times or Arial. I have found many, that neither PS, nor Titler, can properly display, even if they are well-written. When that happens, I often opt for doing the work in Adobe Illustrator, then Placing the AI document into a Photoshop Custom Image, that matches my Project, letting PS Rasterize the Image.