CSS seems to suffer from a problem where all the HUD fonts get messed up.

Its annoying but fixable for most. The following seems to work for most people. Others have found that they have somehow installed the game fonts to the Operating System fonts. When they deleted them, back to normal.

Fix 1. Go to ... C:\Windows\Fonts
The fonts that should not be there are...
cs.ttf
csd.ttf
cslogo.ttf
cstrike.ttf

If they are there...delete them!

Fix 2. Failing that, you could have a custom HUD that is too old?

Time to clean out your game directory, go to....

64 Bit systems...
C:\Program Files (x86)\Steam\steamapps\common\counter-strike source\cstrike\resource
32Bit systems...
C:\Program Files\Steam\steamapps\common\counter-strike source\cstrike\resource

In the "resource" folder only these font files should be there...
cs.ttf
csd.ttf
cslogo.ttf
cstrike.ttf

If there are other .ttf files...delete them!

If the "UI" folder is inside the resource folder...delete it!

In the "scripts" folder, (if it is there, the standard cstrike folder does not have the folder) it is safe to delete the whole folder.

Fix 3. There are also a few more items to try from the Steam support site...

Missing or scrambled text in-game

Question

Answer

Missing Fonts

This issue can occur when Windows fonts are missing or corrupt. The most common being Tahoma. Tahoma can be redownloaded directly from Microsoft here. This is a link to a file stored on an FTP Server. If your browser doesn't support this, it may be necessary to try another browser.

Corrupt or Missing Files

 Your games files may be corrupted or missing.  Please try verifying your Game Cache Files.

Incorrect resolution

Use game launch options to launch with the command -autoconfig.   Please see the following article for instructions: Setting Game Launch Options.

Missing Text in Counter-Strike

• Launch the game.
• Select Options.
• Select the Video tab.
• Set the Renderer to OpenGL.

Want a custom HUD? Mine is up to date.