* Defining "mutually unintelligible" is subjective: What counts as enough unintelligibility to be considered a separate language? There are many dialects and varieties that are difficult to understand for outsiders but still considered part of the same language.
* Language families and dialects: Languages are grouped into families, with branches and sub-branches. Languages within a family often share common roots and some intelligibility, even if they're distinct languages.
* Limited documentation: Many languages, especially those spoken by smaller groups, haven't been thoroughly documented, making it hard to assess their intelligibility.
However, we can consider some data points:
* Ethnologue: This database lists around 7,151 languages worldwide. However, it doesn't explicitly categorize them by mutual intelligibility.
* Language families: There are major language families like Indo-European, Sino-Tibetan, Niger-Congo, etc. Each family has many branches with varying degrees of mutual intelligibility.
* Language diversity: Areas with high linguistic diversity, like Papua New Guinea or the Amazon Basin, often have many languages with very limited mutual intelligibility.
Therefore, rather than a specific number, it's better to understand that there are many languages in the world where speakers would not be able to understand each other without extensive language learning.