[wp-trac] [WordPress Trac] #39210: switch_to_locale() unloads all plugin and theme translations

[WordPress Trac]

#39210: switch_to_locale() unloads all plugin and theme translations
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 Reporter:  gchtr                                |       Owner:  ocean90
     Type:  defect (bug)                         |      Status:  reopened
 Priority:  normal                               |   Milestone:  6.1
Component:  I18N                                 |     Version:  4.7
 Severity:  normal                               |  Resolution:
 Keywords:  has-unit-tests has-patch needs-dev-  |     Focuses:
  note                                           |
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Comment (by flixos90):

 Replying to [comment:71 swissspidy]:
 > We have now already established that there's a bug here causing too many
 calls to `load_textdomain()`. Simple as that. No need for detailed
 performance analysis for other sites or anything.

 I still think it would be interesting to see how the original commit here
 affects performance for the scenarios where it already works as expected,
 so I did a quick test similar to the previous ones where I compared
 6.1-RC2 with 6.1-RC2 with the relevant code replaced with the 6.0.3 code,
 just with translation files present.

 The difference is small, but consistently visible: With de_DE for example,
 with the commit here WordPress took a median of 0.1915s to load, while
 without it it was 0.1956s, so roughly 4ms difference. While there is
 always fluctuation, this seems to indeed be consistent, so it's good to
 see a positive impact of the overall concept.

 > Good news is that I have a [https://github.com/WordPress/wordpress-
 develop/pull/3506 draft PR] fixing this PR. It's like 99% complete.
 >
 > Feel free to to check it out. I will continue looking into it myself
 when my next workday commences.

 I took a look at the PR. I am not too familiar with that code, but it
 seems to me that there is a much simpler solution to the problem than what
 the PR does: The real problem is in
 https://core.trac.wordpress.org/browser/trunk/src/wp-
 includes/l10n.php?rev=54654#L762, which I found out due to further
 testing: Different than my original assessment where I focused on the
 en_US locale, the problem goes actually beyond that: It occurs whenever
 translation files are not present locally, which is certainly possible for
 even locales that are not en_US (e.g. when a plugin or theme is not
 translated yet, or simply when the site has not downloaded the language
 packs yet).

 Simply adding a `$wp_textdomain_registry->set( $domain, $locale, false );`
 above the above line fixes the problem for me, by storing that there is no
 translation file in that situation, the same way it is already done when
 the translation file cannot be imported.

 Potentially this may introduce another problem that I'm unfamiliar with,
 but at least the above change is where I would have started.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/39210#comment:72>
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