No. This font is clerly NOT designed to support all glyphs needed to render any supported language.
For example it MUST NOT be used to display translations. Its purpose is to display only the native language names, exactly those returned by {{#language:code}}
, and only those texts! Its purpose is to allow correct visual identification of languages.
In addition it must be able to render any language code, i.e. lowercase letters a-z, digits 0-9 and the minus-hyphen '-' (needed for language variants)
It may render the uppercase letters, allowed as equivalents for language-codes in BCP47 for use in the lang="" attribute, or any language code supported by Mediawiki on Wikimedia sites, though Wikimedia sites should only use lowercase letters for these codes). For this reason it will include the full printable ASCII range (U+0020..U+007E, i.e. 95 glyphs only); it should probably not include punctuations of ISO88-59-1 or windows-1252 outside ASCII.
The number of needed glyphs is then capped, and is not very large (limited to the list of supported languages).
But if we remove the ASCII characters then the ".autonym" CSS class should contain "font-family: Autonym, sans-serif". But some languages will render inconstantly when some characters are found only in the "Autonym" font, others being in the browser's default fonts for "sans-serif". Their glyph metrics won't match together.
So if we ever remove ASCII charcters from the "Autonym" font, then we MUST remove also all Latin letters, so that they will be all fond in the browser's default fonts for "sans-serif". Caveat: the metrics of Latin letters (in "sans-serif") may no longer match with metrics of other characters needed for other scripts (this will be a problem in case of dual scripts in one language name). So let's keep ASCII completely in that font, with other those Latin letters needed for supported language names.
My opinion is that "sans-serif" is present in the CSS class only for the case where the browser does not load the webfont from ULS, but it should NEVER be used if the Autonym webfont is loaded: the webfont must be complete for all supported languages, even if some of them may be rendered corectly only with the browser's default "sans-serif" font list.
It is absolutely not critical that the Autonym font looks different for displaying languages from the various fonts used for displaying the rest of pages or the UI, as long as it remains in a coherent sans-serif stroke style (for Latin, Cyrllic, Greek), or the default stroke styles most commonly used to display other scripts.
But I agree that all the supported glyphs in the Autonym font should have correct metrics, and good hinting for all resolutions (including small sizes >= 8px, as low as possible). Note that this font should be available in bold and italic for some UI cases (bold needed when the language name is selected in the current page, in a language bar.
Navigation language bars at top or bottom of pages (linking to translated version of the current page) should be deprecated as much as possible : the ULS should be used instead for selecting the page to render, written directly in the language selected for the UI. Pages can autodetect this language (including for their templates), using "autotranslation" based on {{int:lang}} (for example with LangSwitch on Commons or Meta, or with the translate extension).