Traverse each descendant file in the directory tree and replaces all occurrences.

TraverseAndReplace.groovy

/**
 * Usage : Put this script in <ScriptsDir>/project_changed folder. Create a folder if it doesn't exists.
 *
 * @author  Yu Tang
 * @version 0.2
 */

import static org.omegat.core.events.IProjectEventListener.PROJECT_CHANGE_TYPE.*

// prepare
String dir
def replacePair

def skipTraverse(eventType) {
    if (!eventType.metaClass.hasProperty(eventType, 'skipTraverse')) {
        eventType.metaClass.skipTraverse = false
    }
    eventType.skipTraverse
}

switch (eventType) {
    case LOAD:
        // Skip traverse
        if (skipTraverse(LOAD)) {
            LOAD.skipTraverse = false // reset the flag
            return
        }

        dir = project.projectProperties.sourceRoot
        replacePair = [
            [find: /"eng-USA"/, replacement: /"en-US"/],
            [find: /"fra-FRA"/, replacement: /"fr-FR"/]
        ]
        break
    case COMPILE:
        dir = project.projectProperties.targetRoot
        replacePair = [
            [find: /"en-US"/,    replacement: /"eng-USA"/],
            [find: /"fr-FR"/,    replacement: /"fra-FRA"/],
        ]
        break
    default:
        return null // No output
}

String ENCODING = 'UTF-8'
File rootDir = new File(dir)
int modifiedFiles = 0

// options as map
def options = [
    type       : groovy.io.FileType.FILES,
    nameFilter : ~/.*\.xlf/
]

// replacer as closure
def replacer = {file ->
    String text = file.getText ENCODING
    String replaced = text
    replacePair.each {replaced = replaced.replaceAll it.find, it.replacement}
    if (text != replaced) {
        file.setText replaced, ENCODING
        console.println "modified: $file"
        modifiedFiles++
    }
}

def reloadProjectOnetime = {
    LOAD.skipTraverse = true    // avoid potentially infinity reloading loop
    javax.swing.SwingUtilities.invokeLater({
        org.omegat.gui.main.ProjectUICommands.projectReload()
    } as Runnable)
}

// do replace
rootDir.traverse options, replacer

if (modifiedFiles > 0 && eventType == LOAD) {
    console.println "$modifiedFiles file(s) modified."
    reloadProjectOnetime()
}