Templating to aid enriching localized content with HTML

[nilmerg]

Is your feature request related to a problem? Please describe.

Content that can be translated to other languages may sometimes require changes to its structure. Total %d for example may get translated in German to %d Gesamt.
There may also be entire sentences which get translated. If they're translated to a language such as Arabic the sentence may reversed as textual content in Arabic is written from right to left (RTL).

To make this possible, source code must mark the entire content in a single message as localizable. e.g. t('Total %d'). String concatenation is not possible.

In case a developer wants to enrich parts of the content with HTML, this is currently not possible in such a case. Say I'd want to put Total in a span to style it differently, the result would look like this: (Example taken from https://github.com/Icinga/icingadb-web/pull/94/files)

<span class="meta">Total</span> %d

Though, this would require rendering the HTML instantly and allow the translator to change the markup. Both are undesirable side-effects.

Describe the solution you'd like

There is already the possibility to format content using the class FormattedString. Why not extend it so that it supports a simple form of templating. This could look like this:

{{#total}}Total{{/total}} %d

Given the following code:

FormattedString::create(
    '{{#total}}Total{{/total}} %d',
    ['total' => Html::tag('span')]
);

The result could be:

<span>Total</span> 1234

and in German:

1234 <span>Gesamt</span>

[lippserd]

I'd stick with Mustache here and begin the block with {{#total}}...