I am also working with a naturally unicode language and the easiest and sure fix as follows:

1-] Download a unicode supporting true type font. An example is OpenDyslexic-Regular.

Here is GitHub repository for it.

2-] You either work in that directory you downloaded .ttf while in Python, or give the complete path.

3-]

pdf = FPDF()
pdf.add_page()
pdf.add_font("OpenDyslexic-Regular", "", "./OpenDyslexic-Regular.ttf", uni=True)
pdf.set_font("OpenDyslexic-Regular", "",8)
pdf.multi_cell(0, 10, txt="çiöüşp alekrjgnnselrjgnaej")
pdf.output("##.pdf" )

4-]