Labels formatting (via tags) in locallang.xlf - typo3

Question

Whenever a part of a language label needs to be somehow highlighted, what is considered as best practice here?
I'm usually trying to avoid html tags in language labels as far as possible by splitting label into a parts and wrapping into corresponding tags in Fluid.
In worst case label is wrapped with CDATA:
<trans-unit id="my.label">
<source><![CDATA[Here comes a <strong>bold text</strong> and then <em>italic</em> and now <span class="fancy">fancy styled</span> stop]]></source>
</trans-unit>
But this mixes content and presentation, which can bring pain afterwards, when CSS is refactored and some classes are renamed.
Another solution, coming into my mind, is to move all the texts, that may contain html tags, out of XLF to either plugin's FlexForm RTE field or some configuration record with RTE fields. But it also looks rather like hack.
How do you solve such an issue usually?

Answer 1

For me there are some possible options, depending on the kind of text.
1.) Avoid HTML as much as possible
2.) If this HTML is wrapped around any arguments, move the HTML out and use it as argument for the <f:translate /> ViewHelper.
3.) Sometimes it is hard to use arguments as the translation is just different and I then use different partials/sections for the different languages and don't use any language file.
4.) I use the CDATA approach.

Answer 2

An addition to Georg Ringer's answer (whose point 1 is definitely the way to go, if at all possible):
5.) Use what XLIFF offers. XLIFF 1.2 has elements to mark tags inside translatable content - to be precise, it has too many such elements. One possible representation of your example would be
<trans-unit id="my.label">
<source>Here comes a <bpt id="1"><strong></bpt>bold text<ept id="1"></strong></ept> and then <bpt id="2"><em></bpt>italic<ept id="2"></em></ept> and now <bpt id="3"><span class="fancy"></bpt>fancy styled<ept id="3"><span></ept> stop</source>
</trans-unit>
This looks messy in code, but it has the advantage that an XLIFF aware translation editor will present this to your translators in a way that is easy for them to work with, like this:
.
The translator will be able to move these tags if the text order needs to be changed in the target language, and they can delete these purple tags in whole if they don't make sense in the target language: for example some complex Chinese characters look awful in bold face. They will not be able to delete parts of tags either.

Answer 3

One possible solution could be the use of parameters in the translation strings. Those parameters could be filled with translated strings which are wrapped in tags (by TS or fluid). This might result in a very complex translation handling as the strings are broken down to multiple strings (which might partially loose context).
Another solution could be the use of markers (like ###B### for <b>and ###_B### for </b>) for the tags which are replaced at the end (and which could vary for different devices). This also is complex and needs a good configuration and invents something like a further markup.