Language rarely changes all at once.
Words and abbreviations can remain in use because people continue to understand them, even when the original expression becomes less common.
“WC” is a perfect example.
In many parts of Europe, the abbreviation remains familiar on signs in public places.
Travelers may see it at airports, railway stations, restaurants, museums, shopping centers, hotels, and tourist attractions.
Its usefulness comes from its simplicity.
Two letters take up very little space on a sign.
They can also be easier to recognize quickly than a longer word, particularly in places where people speak multiple languages.
Imagine an international airport with passengers arriving from dozens of countries.
A sign cannot realistically display a different word for every language.
Symbols are often used for this reason, but abbreviations such as WC can also serve as familiar visual shorthand in many regions.
There is another interesting reason the abbreviation survives: architectural and plumbing terminology often preserves older language.
A building plan may still distinguish a WC from other areas such as a bathroom, shower room, utility room, or washroom.
In some contexts, the terminology is therefore more technical than conversational.
This does not mean that “WC” has exactly the same meaning everywhere.
Cultural differences matter.
In some countries, people may use “WC” primarily on signs while using an entirely different term in everyday conversation.
In other countries, “toilet,” “bathroom,” “restroom,” or local-language equivalents are much more common.
The important point is that WC has become a recognizable international abbreviation even though the full phrase “water closet” is no longer common in ordinary English conversation.
This is similar to many other abbreviations that have survived through changing language.
People often continue using a shortened form because it is convenient, familiar, and easy to recognize.
In the case of WC, more than a century of architectural and cultural history has helped keep those two letters alive.