Geoserver SLD - priority option displays multiple labels

Question

I'm using priority option for labels in my geoserver SLD stylesheet because I have multiple overlapping points.

<Priority>
  <ogc:PropertyName>language</ogc:PropertyName>
</Priority>

The problem is, geoserver renders both labels if there are two overlapping points. The priority one is above, and the another one is below.

I need only one of those labels (top priority one) to be rendered.

EDIT:

Whole TextSymbolizer looks like this:

<TextSymbolizer>
        <Label>
          <ogc:PropertyName>pisanjeimena</ogc:PropertyName>
        </Label>
        <Priority>
          <ogc:PropertyName>language</ogc:PropertyName>
        </Priority>
        <VendorOption name="group">false</VendorOption>
        <VendorOption name="labelAllGroup">true</VendorOption>
        <VendorOption name="spaceAround">10</VendorOption> <!--allow labels to overlap-->
        <!--<VendorOption name="followLine">true</VendorOption>--> <!--option forces a label to follow the curve of the line-->
        <VendorOption name="maxDisplacement">30</VendorOption> <!--option controls the displacement of the label along a line-->
        <VendorOption name="repeat">100</VendorOption> <!--option determines how often GeoServer displays labels along a line-->
        <VendorOption name="autoWrap">150</VendorOption> <!--option wraps labels when they exceed the given width (in pixels)-->
        <!--<VendorOption name="conflictResolution">false</VendorOption>--> <!--conflictResolution option to false causes this label to bypass conflict resolution-->
        <VendorOption name="goodnessOfFit">0.3</VendorOption>      
        <Halo>
          <Radius>2</Radius>
          <Fill>
            <CssParameter name="fill">#FFFFFF</CssParameter>
            <CssParameter name="fill-opacity">0.6</CssParameter>
          </Fill>
        </Halo>
        <Font>
          <CssParameter name="font-family">Arial</CssParameter>
          <CssParameter name="font-size">12</CssParameter>
          <CssParameter name="font-style">normal</CssParameter>
          <CssParameter name="font-weight">bold</CssParameter>
          <CssParameter name="fill-opacity">0.6</CssParameter>
        </Font>
        <LabelPlacement>
          <PointPlacement>
            <AnchorPoint>
              <AnchorPointX>0.5</AnchorPointX>
              <AnchorPointY>0.0</AnchorPointY>
            </AnchorPoint>
            <Displacement>
              <DisplacementX>0</DisplacementX>
              <DisplacementY>5</DisplacementY>
            </Displacement>
          </PointPlacement>
        </LabelPlacement>
        <Fill>
          <CssParameter name="fill"><ogc:PropertyName>boja</ogc:PropertyName></CssParameter>
        </Fill>             
      </TextSymbolizer>

Language property that is used in <Priority> is numerical value (language ID). Language with higher ID should be a priority one.

Answer 1

You have confused the label placement algorithm by giving it too many instructions and choices.

    <VendorOption name="group">false</VendorOption>
    <VendorOption name="labelAllGroup">true</VendorOption>

You can leave these two out as they are the defaults.

    <VendorOption name="spaceAround">10</VendorOption> <!--allow labels to overlap-->

This doesn't do what your comment suggests you think it does. If you want labels to overlap (and you probably don't) then set a negative value.

    <VendorOption name="maxDisplacement">30</VendorOption> <!--option controls the displacement of the label along a line-->

Again, this is unlikely to be what you want, as it allows the renderer to jiggle labels around (up to 30px) to get more labels in. It is almost certainly where your problem occurs. Thus, you can get two (or more) labels for a set of stacked points.

    <VendorOption name="repeat">100</VendorOption> <!--option determines how often GeoServer displays labels along a line-->

This only applies to lines, so leave it out.

    <VendorOption name="autoWrap">150</VendorOption> <!--option wraps labels when they exceed the given width (in pixels)-->

This is fine (assuming your labels have spaces in them.

    <!--<VendorOption name="conflictResolution">false</VendorOption>--> <!--conflictResolution option to false causes this label to bypass conflict resolution-->

Turning conflictResolution off like this allows the renderer to draw as many labels as it likes as it can ignore all the other settings - thus, all your points will be labelled. Don't turn it off unless you are very sure you know what you are doing.

    <VendorOption name="goodnessOfFit">0.3</VendorOption>    

This is to allow the renderer to exceed the bounds of the polygon it is labeling inside, it has no effect on points such as you are using so leave it out.