i18n: Support subexpressions of type (t "text") in Handlebars.

docs/translating/internationalization.md

@@ -241,6 +241,14 @@ Handlebars [helpers][] that Zulip registers.  The syntax for simple strings is:
 {{t 'English Text' }}
 ```
 
+If you are passing a translated string to a Handlebars Partial, you can use:
+
+```
+{{> template_name
+    variable_name=(t 'English Text')
+    }}
+```
+
 The syntax for block strings or strings containing variables is:
 
 ```

zerver/management/commands/makemessages.py

@@ -48,6 +48,8 @@ strip_whitespace_left = re.compile("\\s+(%s-\\s*(endtrans|pluralize).*?-?%s)" %
 regexes = [r'{{#tr .*?}}([\s\S]*?){{/tr}}',  # '.' doesn't match '\n' by default
            r'{{\s*t "(.*?)"\W*}}',
            r"{{\s*t '(.*?)'\W*}}",
+           r'=\(t "(.*?)"\)(?=[^{]*}})',
+           r"=\(t '(.*?)'\)(?=[^{]*}})",
            r"i18n\.t\('([^']*?)'\)",
            r"i18n\.t\('(.*?)',\s*.*?[^,]\)",
            r'i18n\.t\("([^"]*?)"\)',

zerver/tests/test_i18n.py

@@ -155,6 +155,9 @@ class FrontendRegexTestCase(TestCase):
             ("{{t 'english text' }}, 'extra'}}",
              'english text'),
 
+            ("{{> template var=(t 'english text') }}, 'extra'}}",
+             'english text'),
+
             ('i18n.t("english text"), "extra",)',
              'english text'),