Indeed Mark, if you use DITA, you can use the xml:lang attribute for this.
For example, I'm writing a Dutch user guide for an English software product. In that case, I will set the xml:lang attribute on my <topic> elements to Dutch (xml:lang="nl-nl"), but I use special elements to refer to the user interface of the software, for example <uicontrol>. The xml:lang attributes for my <uicontrol> elements will be set to <en-us>. The spell-checker will switch between my English and Dutch dictionary automatically.
And my translators will know that they will have to be extra careful when they translate the text of my <uicontrol> elements.
Great feature!
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Yves Barbion
www.scripto.nu