Use transliterator to slugify non-ASCII strings

Description

Use transliteration for files which contain non-ASCII characters. (This is not a translation)

Motivation and Context

Follow-up to a comment from !1715 (merged) to improve the slugify function.

How Has This Been Tested?

• Thai: "Love: " + "รัก".slugify() -> Love: rak
• Greek: "Love: " + "Αγάπη".slugify() -> Love: agape
• Chinese (Simplified): "Love: " + "爱".slugify() -> Love: ai

Types of changes

• Enhancement (non-breaking change which cleans up / improves existing functionality)

Checklist

• I have read the CONTRIBUTING section of the README document.