For Visualforce we are using custom labels as described here:
https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_variables_global_label.htm
The usage is very simple:
{!$Label.yourLabelName}
Labels are a very important building brick if it comes to I18n/L10n and translations using Translation Workbench.
Are they supported in Lightning Components yet?