New i18n mechanism as separate transformation step

Description

Implement a new i18n translation mechanism as separate XSLT transformation step.
Text can be given multi-language in webpages or xed or xslt files.
The last transformation step reduces the text to the language currently used.
No need to duplicate large html sections in webpages any more.
No need to have different i18n mechanisms in webpage, xed and xslt.
Syntax should be as simple and compact as possible.

Usage:

It is also possible to use keys from messages.properties:

Here is a sample webpage:
https://duepublico2.uni-due.de/content/index.xml?XSL.Style=xml

Environment

None

Assignee

Frank Lützenkirchen

Reporter

Frank Lützenkirchen

Labels

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URL

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External issue ID

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Components

Fix versions

Priority

Medium
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