* What constitutes a dialect is subjective. There's no clear-cut line between a dialect and a separate language. Linguists often disagree on what defines a dialect, and the level of difference needed to be considered a separate language varies.
* Dialects are constantly evolving. Language is dynamic, and new dialects are emerging while others are disappearing.
* Data collection is incomplete. Not all languages and dialects have been thoroughly documented.
However, some estimates place the number of dialects in the millions.
For example, the Ethnologue, a comprehensive database of languages, lists over 7,100 languages, but it is important to remember that many of these languages have multiple dialects. Therefore, the actual number of dialects is likely much higher.
Ultimately, the number of recognized dialects is a constantly shifting figure, and an exact number is impossible to determine.