Each character has a numeric value. Way back at the dawn of time (several decades ago) a standard character set was defined with values from zero to 126. These are the unaccented characters, numbers, and punctuation marks. The character set was called "ASCII", the American Standard Code for Information Interchange, which tells you something about its parochial origins.

Later, people started adding characters between 127 and 255 to accommodate (primarily) European use of accented characters. There are two problems with this: The upper character set has only been loosely standardized, and many fonts produce different characters in the upper range; and keyboard layouts and characters produced by certain keys have varied by nationality. You're probably using a French keyboard which shows the accented characters.

Because of this, HTML defines a whole bunch of special character codes that the browser (usually) knows how to translate into whatever font your computer is using. These are codes like ™ that produce, in this case, a trademark symbol in whatever the current font is. Apropos to your use of accented characters, there are a whole bunch of those, too, like à which produces an A with a tilde (Ã).

There are hundreds of these, and unfortunately nobody's ever done a good job of documenting them in one place. Here is one halfway decent list.

While your accented characters seem to work inside posts, bear in mind that you're looking at them on a European computer with European character sets installed. Other people may well see entirely different characters than you do. The best way to ensure that everybody sees the same characters is to use those special HTML ampersand sequences....even though it's a huge pain in the derriére.