What is the RU file format?
A .ru file is a Java development environment ancillary file. It allows users to use Cyrillic (Russian) font glyphs in place of standard Latin fonts. Details regarding specific font mappings can be found in the font.properties.ru configuration file bundled with the JRE.
The Java Virtual Machine uses so-called properties files, which are loaded by the program on launch. To access a properties file at the code level, the java.util.Properties class must be instantiated - this approach allows a developer to use data from .ru files dynamically. Under the classic text convention, Cyrillic characters were encoded as \uXXXX Unicode escape sequences within ISO-8859-1 text; modern Java projects write locale files directly in UTF-8.
The .ru file follows the standard .properties key=value format: each line holds a key=value or key:value pair, and lines starting with # or ! are treated as comments. It is a plain-text file that any text editor can open; the JVM reads it at runtime through the java.util.Properties loader or as part of a ResourceBundle localization workflow.
Security & safety
RISK: LOWA .ru properties/text file is inert plain text with no executable code, so it is safe to open and read in any editor. The only real cautions are about misidentification: '.ru' is an ambiguous extension (also a country TLD and used by unrelated programs), so an unknown .ru is not necessarily this Java resource - open it in a text editor to see what it actually contains before assuming. If a file you expected to be text is binary/garbled, it is a different format.
Format details
in a nutshell- RegRun / Greatis registry-startup file (.ru) - Some Windows startup/registry-monitoring tools have used .ru data files; unrelated to Java properties.
- Generic Russian text / localization resource - A plain Russian-language text or translation resource for various apps, identified only by the .ru locale suffix.
Programs that open RU files
Windows2 apps
Java Runtime Environment
Free The JRE doesn't 'open' the file for viewing - the Java application reads it at runtime via java.util.Properties. Install it only because a Java program needs it; to inspect the file, use a text editor.
Windows Notepad / Notepad++ / VS Code
Free Open the .ru as plain text to read/edit the key=value entries. VS Code/Notepad++ handle UTF-8 and show Cyrillic correctly. 
macOS2 apps
Java Runtime Environment
Free Runtime resource for Java apps; install only if a Java program requires it. Inspect the file in a text editor, not the JRE. 
Linux2 apps
Java Runtime Environment
Free Runtime resource read by Java applications; not a viewer. Use a text editor to inspect.
Any text editor (gedit, vim, VS Code)
Free Open the .ru as plain text to read/edit the key=value pairs. Technical details
deep spec| File category | Plain-text Java properties file carrying Russian font mappings or localized strings |
| Character encoding | Historically ISO-8859-1 with \uXXXX Unicode escapes for Cyrillic; UTF-8 in modern Java |
| Locale suffix | '.ru' marks the Russian (ru) locale variant of a base properties bundle (e.g., messages_ru.properties) |
| Comment syntax | Lines beginning with '#' or '!' are treated as comments and ignored by the parser |
| Key-value delimiter | '=' or ':' separator; surrounding whitespace is trimmed by the parser |
| MIME type | text/x-java-properties (also accepted as text/plain) |
| Runtime loader | java.util.Properties class or java.util.ResourceBundle; loaded by the JVM at startup or on demand |
| Primary use | Russian font-to-system-font mappings (font.properties.ru) or Russian-locale UI label translations |
| Multi-line values | A backslash at end of line acts as a continuation character, allowing a single value to span multiple lines |
| Escape sequences | Non-ASCII characters encoded as \uXXXX code-point escapes in the classic format; raw UTF-8 in modern usage |
| Typical file size | Under 1 KB for font configuration; up to a few hundred KB for a full UI string table |
| Platform support | Any OS running a Java Runtime Environment (Windows, macOS, Linux, and others) |
| Binary signature | None - plain text with no magic bytes; identified by the .ru suffix and locale context |
| Superseded by | UTF-8 .properties files and XML-format ResourceBundle files in contemporary Java i18n workflows |
| Released | Java properties mechanism (java.util.Properties), 1995+; '.ru' as a Russian-locale suffix |
| Open standard | Yes · royalty-free |
| Specification | docs.oracle.com |
RU conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about RU files.
