The differences between Tahoma and what is already there on this blog, http://ibrahimbadawi.wordpress.com/ is about as close to zero as you will get. You need to include additional fonts in the stack to keep the browsers from just substituting whatever they want, but the last are exactly what is there now.
h2.post-title {
font-family: Tahoma, Arial, Helvetica, sans-serif;
font-size: 100%;
}
.post-content p {
font-family: Tahoma,Arial,Helvetica,sans-serif;
font-size: 100%;
}
Bold text is not separately defined, so it will inherit the font settings set in one of its parent divs.
To have separate fonts and such for the other language, you will have to create rules in the CSS and then you will have to declare a class in a div at the beginning of each post or page in the other language, and end the post with a closing div tag as follows.
<div class="other">
all your other language text and such here
</div>'
You would then create a rule in the CSS similar to this:
.other {
font-family: [enter your fonts here];
font-size: 100%;
}`