There's really no such thing as a 'unicode font'. I don't think any one font covers all possible characters in all languages, as unicode encoding covers many character sets. For example sanskrit characters are wildly different from Chinese characters, or hieroglyphics. They would have to install many fonts to cover all possible languages, and they are probably waiting to see what the demand really is before putting any work into determining how to represent character encodings in a bunch of different fonts (including languages that read right to left, instead of left to right, etc.).
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