This PR was squashed before being merged into the 3.4 branch (closes #31266).

Discussion
----------

[Translator] Load plurals from po files properly

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10152 (comment)
| License       | MIT
| Doc PR        |

Plurals were not handled correctly when loading po files.
```
msgid "foo"
msgid_plural "foos"
msgstr[0] "bar"
msgstr[1] "bars"
```

Before, the po entry above was treated as two entries, which doesn't make sense:
```
'foo' => 'bar'
'foos' => 'bar|bars'
```

With this PR, it is treated as one entry:
```
'foo|foos' => 'bar|bars'
```

Commits
-------

6b69a99 [Translator] Load plurals from po files properly

This PR was merged into the 3.4 branch.

Discussion
----------

[Translator] Load plurals from mo files properly

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #10152 (comment)
| License       | MIT
| Doc PR        |

Plurals were not handled correctly when loading mo files.
```
msgid "foo"
msgid_plural "foos"
msgstr[0] "bar"
msgstr[1] "bars"
```

Before, the mo entry above was treated as two entries, which doesn't make sense:
```
'foo' => 'bar'
'foos' => '{0} bar|{1} bars'
```

With this PR, it is treated as one entry:
```
'foo|foos' => 'bar|bars'
```

This PR does the same as #31266, just for mo files instead of po files. Note, however, that the old behavior differed between po and mo files: `'foos' => 'bar|bars'` for po files and `'foos' => '{0} bar|{1} bars'` for mo files.

Commits
-------

97d28b5 Load plurals from mo files properly

…tadly)

This PR was submitted for the master branch but it was squashed and merged into the 4.4 branch instead (closes #31269).

Discussion
----------

[Translator] Dump native plural formats to po files

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #29963, #10152
| License       | MIT
| Doc PR        |

Implementing support for dumping to the native po plural format.

```
'foo|foos' => 'bar|bars'
```

Before, the entry above was dumped directly:
```
msgid "foo|foos"
msgstr "bar|bars"
```

With this PR, it is dumped using the native po plural format:
```
msgid "foo"
msgid_plural "foos"
msgstr[0] "bar"
msgstr[1] "bars"
```

Strings using explicit rules or contain more than 2 pluralization forms are still dumped directly, as the po format does not support such cases:

```
'{0} no foos|one foo|%count% foos' => '{0} no bars|one bar|%count% bars'
```

```
msgid "{0} no foos|one foo|%count% foos"
msgstr "{0} no bars|one bar|%count% bars"
```

This PR complements #31266, fixing loading of native po plural formats.

Commits
-------

dc31739 [Translator] Dump native plural formats to po files