Language Support

Improving Inkscape support for internationalized/multi-lingual SVG

There are two distinct language settings:

• the user's preferred language(s) (affects systemLanguage conditional test)
• declaring the document/element language (xml:lang); for SVG 2, this would be used as a conditional switch for <title> and <desc>

systemLanguage & conditional tests

• The systemLanguage attribute is used to only show certain content if it matches the user's preferred language, usually within a `<switch>` element. In a browser, the user's preferred languages are the same as those sent in HTTP headers.

Read support

• Support for displaying conditional SVG is implemented within conditions.cpp, which uses SPDocument.getLanguage() (document.cpp) to find the user's preferred language (as set in the preferences dialog)
  • BUG: If the user's preference setting is "System Default" (the default), it does not match the actual language code! See Bug #1249423
  • possible bug: According to the specs, the user's preferred language shouldn't be a document property, it should be a UI property. However, if Inkscape in the future implements ways to create <switch> elements, you would definitely want to swap between languages on a document basic (instead of resetting their UI settings and restarting Inkscape).
  • Potential enhancements:
  1. The user should be able to set alternate languages in preferences, similar to how browsers set multiple values for the HTTP Accept-Language header (and use the same values for <switch>).
  2. The user should be able to temporarily swap the preferred language for any document view, to see how the graphic looks like for others.
  3. If the conditional tests all fail within a <switch>, the user could be prompted to select which language they prefer.

Write support

• No UI support currently for creating <switch>, this would all be enhancement
• Best use case would be within individual <text> elements, to switch between languages
• would need a way to swap the canvas view to show the different languages (e.g., temporarily swap the user preferred language for that document)
• would need a way to specify which text should be used as default, and then to store the language information (as xml:lang probably). In the SVG markup, the only way to create a default is to give it as the last element in a <switch>, and don't give it a systemLanguage attribute

xml:lang

• The xml:lang attribute defines the language of text content (visible text or alternative text). It is used in advanced text layout, by screen readers, and by web translation tools.

Read support

• For reading existing files, this is relevant for
  1. passing information to OS Accessibility APIs
  2. rendering text in certain scripts where the Unicode characters map to different glyphs depending on the language
• Would need some typography experts to confirm that there is already support in underlying text layout libraries (HarfBuzz/Pango), and what info needs to be forwarded to them to get the correct rendering.
• The code for figuring out the current language is already used in CSS to match the :lang() pseudo-selector (cr-sel-eng.c). If there are no bugs there, it can hopefully be generalized for finding out the language code and passing it to text layout.

Write support

Basic support:

• There should be a document-level property that can be set (e.g., xml:lang attribute on the <svg> element) see Bug #170340
• Currently, there is a language field in the document metadata, but this is not used for xml:lang.
• By default, the document language should be the user's preferred language at the time the document is created, but it should be easy to change.
• Ideally, you should be able to set xml:lang on individual elements or groups, in order to define multi-lingual documents.
• For text elements, this could be in the font & text dialog, but more generally it would be in object properties
• However, you should also be able to set language on a <tspan>, so that would mean allowing the user to select some text and then assign a language value.
• Would want to have a "use document language" checkbox (with the current document language setting clearly stated); if unchecked, you would then have a drop-down list/text box to set a different language for this element. Technically, this shouldn't be "document" language, but "parent element" language (since you could set language on groups or similar); not sure what a better wording would be.

Making use of language for added features:

• Once Inkscape is able to keep track of the document language, and the user is able to set the document language, then it would be possible to implement spelling/grammar checking or other language-based features.
• For spellcheck, there is even a functionality in GTK: see http://wiki.inkscape.org/wiki/index.php/SpellCheckForTextNodes. text-edit.cpp has a TODO to use a computed value of xml:lang in gtkspell_set_language().

Multi-lingual accessible text:

• For SVG 2 multi-lingual title/desc, you would need a way to
  1. add additional title/desc in the object properties dialog,
  2. set the language for each (this should be *required* for having multiple title/desc elements) and
  3. specify which one is the default
• For title/desc, the default *would* have a lang attribute (note, SVG 2 spec currently uses `lang` not `xml:lang`), and would be the *first* such child element in the DOM.