i18N in SLD

This section describes how to specify metadata (titles and abstracts) in different languages in SLD documents.

Metadata in different languages

GeoServer extends Title and Abstract sections, so that text in different languages can be included.

This is an example of the syntax to use:

<Title>This is the default title
  <Localized lang="en">English title</Localized>
  <Localized lang="it">Titolo in italiano</Localized>
</Title>

A default text (This is the default title in the example) and a set of Localized sections, one for each language that you want to support.

Each Localized section specifies the language (using a two letter abbreviation in the lang attribute) and the related text.

Currently, GeoServer supports localized text in SLD in WMS GetLegendGraphic requests (legends that contain labels are rendered using the requested language, if a LANGUAGE parameter is added to the request, e.g. LANGUAGE=it).

Using the language function

GeoServer provides a language function that can be used to get the LANGUAGE requested in GetMap or GetFeatureInfo request. The function can be used to generate maps whose symbology is language dependent.

Here is an example providing labels in multiple languages, integrating the language function with Recode e.g:

 <TextSymbolizer>
        <Label>
          <ogc:Function name="Recode">
            <ogc:Function name="language"/>
            <ogc:Literal/>
            <ogc:PropertyName>name_default</ogc:PropertyName>
            <ogc:Literal>en</ogc:Literal>
            <ogc:PropertyName>name_en</ogc:PropertyName>
            <ogc:Literal>it</ogc:Literal>
            <ogc:PropertyName>name_it</ogc:PropertyName>
            <ogc:Literal>fr</ogc:Literal>
            <ogc:PropertyName>name_fr</ogc:PropertyName>
          </ogc:Function>
        </Label>
        <Fill>
          <CssParameter name="fill">#000000</CssParameter>
        </Fill>
</TextSymbolizer>

The empty <ogc:Literal/> elements acts as the default language, matching a value with a missing language parameter. If there is no default value,the default language will be returned. See Internationalization (i18n) for details on Default Language.

It is also possible to use the language function in a rule filter, filtering rules for both rendering and legend production purposes. This one shows how to refer to different symbols based on the current language:

<Rule>
  <ogc:Filter>
    <ogc:PropertyIsEqualTo>
      <ogc:Function name="language"/>
      <ogc:Literal>it</ogc:Literal>
    </ogc:PropertyIsEqualTo>
  </ogc:Filter>
  <PointSymbolizer>
    <Graphic>
      <ExternalGraphic>
        <OnlineResource xlink:type="simple" xlink:href="it_symbol.png"/>
        <Format>image/png</Format>
      </ExternalGraphic>
      <Size>32</Size>
    </Graphic>
  </PointSymbolizer>
</Rule>
<Rule>
  <ogc:Filter>
    <ogc:PropertyIsEqualTo>
      <ogc:Function name="language"/>
      <ogc:Literal>de</ogc:Literal>
    </ogc:PropertyIsEqualTo>
  </ogc:Filter>
  <PointSymbolizer>
    <Graphic>
      <ExternalGraphic>
        <OnlineResource xlink:type="simple" xlink:href="de_symbol.png"/>
        <Format>image/png</Format>
      </ExternalGraphic>
      <Size>32</Size>
    </Graphic>
  </PointSymbolizer>
</Rule>

Specifically for the external graphics, if the external symbols are all co-located, and follow a naming convention including the language identifier, then it’s also possible to embed the language in the symbol URL:

<Rule>
  <PointSymbolizer>
    <Graphic>
      <ExternalGraphic>
        <OnlineResource xlink:type="simple" xlink:href="${language()}_symbol.png"/>
        <Format>image/png</Format>
      </ExternalGraphic>
      <Size>32</Size>
    </Graphic>
  </PointSymbolizer>
</Rule>
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