Web browser: ---
            Bug ID: 59958
           Summary: ULS loading language-specific fonts for interlanguage
           Product: MediaWiki extensions
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Keywords: performance
          Severity: normal
          Priority: Unprioritized
         Component: UniversalLanguageSelector
    Classification: Unclassified
   Mobile Platform: ---

Created attachment 14294
Waterfall diagram showing impact on latency and resource utilization

On <>, UniversalLanguageSelector
loads just under half a megabyte of fonts (490.2 Kb). By comparison, the
combined size of all other resources -- that is, *all* javascript, CSS, images
and text -- is 346 Kb.

The impact on page performance is severe. It is clearly noticeable even on a
high-bandwidth, low-latency connection. The attached image shows the font
requests saturating bandwidth, then CPU as they are retrieved and rendered.

More details here: <>

WebKit browsers hide text until the font is available. This causes the
interlanguage links for which ULS is overriding the system default font
selection to appear in one font, vanish for several seconds, and then re-appear
in a different font. I recorded this on my laptop:
<>. Note that I am using a
bleeding-edge browser version and connecting to the internet via a broadband

In my assessment, the frequency and regularity with which this issue has
recurred makes it clear that ULS's strategy for loading web fonts is
fundamentally misguided. I do not consider a selector exemption to be an
adequate solution to this bug.

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