There are a number of tools you can use to translate WordPress projects. However locale packages are built from the translations on translate.wordpress.org (that runs on GlotPress). So no matter which tool you choose, after you finish translating, you will need to go to translate.wordpress.org and import the relevant gettext files.
You can get to know the tools you can use in the descriptions below:
The translation consistency tools will help you analize if an original term is translated consistently throughout your locale. You can enter a term and you will see a list of its different uses in your language. Ideally, a term should be added to a locale’s Glossary and used consistently across the whole project.
Each team needs to have their own Glossary to help new translators get started and keep the translations of WordPress, plugins and themes consistent. GlotPress has a built in Glossary that allows translators to see the proper translation of an original term while translating in translate.wordpress.org if that term is a part of the glossary. See the list of glossaries and style guides per locale.
The addon for FireFox and Chrome will link GlotPress to the glossary of your local language. So while translating strings you have an immediate view on how the words should be translated in your language to keep the consistency.
Other translation tools
Some teams prefer to use other translation tools and import translations into translate.wordpress.org after. See a list of other available tools you can use to translate WordPress. Please have in mind that the recommended way of translating WordPress is through translate.wordpress.org.