Add CurseMaven to your dependency repositories

repositories {
    maven {
        url = "https://www.cursemaven.com"
    }
}

Then add Server-Translations to your dependencies

dependencies {
    modCompile "curse.maven:server-translations:3045346"
}

Translation files path should looks this data/<modid>/lang/<language code>.json

Simply create a new TranslatableText using the key.

WIP