Internationalization and localization
Internationalization (i18n) refers to the process of extracting strings from source code and presenting them as properties with a set of values.
Localization (l10n) refers to the process of translating values of these properties into target languages.
Keys and values for the target languages are stored in dedicated properties files, which can be combined into a resource bundle for convenience. IntelliJ IDEA can recognize hard-coded string literals and suggest to extract them into the corresponding properties files.