[SalesForce] Custom Labels and tests

In apex:page there is an attribute 'language' which you can set as the language of your choice/requirement to override the users language.

Check this link

language

The language used to display labels that have associated translations in Salesforce. This value overrides the language of the user viewing the page. Possible values for this attribute include any language keys for languages supported by Salesforce, for example, "en" or "en-US".

From documentation seems it should be possible. I haven't tried it out though.

It simply means:

1. When you have a label attribute, the component level error message would show error in context label passed in attribute.
2. When your have a empty label attribute or does not have a label attribute at all, it would not show any message with the default field's label.

Difficult to understand; maybe it would be clear when you try the example.

Output on click of save when email is empty (code at the end)-

Note: Error message for second and third sections/input are same (as apex:pageMessage doesn’t show duplicate message), default message with field's label; only difference is in #3 we have empty label hence it doesn't show a field label because its expecting us to add.

Code for illustration:

<apex:page standardController="Contact">
    <apex:form id="form">
        <apex:pageMessages></apex:pageMessages>
        <apex:pageBlock title="Quick Edit: {!Contact.Name}">
            <apex:pageBlockSection title="1. Dynamic Label" columns="1">
                <apex:inputText value="{!Contact.Email}" 
                    label="{!Contact.FirstName + '’s Email'}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="2. No label" columns="1">
                <apex:inputText value="{!Contact.Email}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="3. Empty label" columns="1">
                <apex:inputText value="{!Contact.Email}" label="" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockSection title="4. From custom Label" columns="1">
                <apex:inputText value="{!Contact.Email}" 
                    label="{!$Label.Label_Contact_Email}" required="true"/>
            </apex:pageBlockSection>
            <apex:pageBlockButtons >
                <apex:commandButton action="{!save}" value="Save" rerender="form"/>
            </apex:pageBlockButtons>
        </apex:pageBlock>
    </apex:form>
</apex:page>