Judith Schmid 

The old one isn't available anymore because it is no longer supported by Windows.  It was the Arial Unicode MS font family.  You can find an explanation of why it's no longer available here: https://learn.microsoft.com/en-us/typography/font-list/arial-unicode-ms  But the essence of it is that it became impossible for them to support all the unicode characters  that are expected in a single font family like this.

So, we moved to Segoe UI (https://learn.microsoft.com/en-us/typography/font-list/segoe-ui) which is preferred by Microsoft and supports a wider range of unicode characters.  Segoe UI is designed to be able to display a broad array of characters and symbols from different languages and scripts, making it extremely versatile for global applications like Trados Studio which supports so many languages and usecases.  The font family includes multiple variants such as Segoe UI Symbols, Segoe UI Mono, Segoe UI Historic, Segoe UI Variable, and Segoe UI Emoji.  Each variant is tailored for specific uses or stylistic preferences. For example:

• Symbols variant contains a wide range of symbols.
• Mono is a monospaced variant, where each character takes up the same horizontal space, ideal for code.
• Historic covers historical scripts and symbols.
• Variable is a newer type that allows for fine-tuned font weight and style adjustment.
• Emoji contains emoji characters, often in full color.

We also implemented a new rendering engine into Trados Studio that works seamlessly with Segoe UI.  A rendering engine is software that draws text and images on the screen and the integration with Segoe UI means that the engine can intelligently select the best variant of Segoe UI for a given context without explicit instructions from the developer.  To give you an example of why this is important... with the activation of colored fonts the system can automatically display emojis in color without requiring developers to specify the use of the emoji variant of the font.  This simplifies the process of incorporating emojis into text and ensures they are rendered in their intended style automatically.

So that's why we had to stop using the old one... it just wasn't fit for purpose in today's world.

You can change yourself though and select a different font if you find that Segoe UI isn't to your liking.  Do that under Editor -> Font Adaptation in the Options.  Select the languages you want to use your preferred font for and apply them.  Note that when you do this and then revisit the settings, it will always look like this:

But the ones you set will remain set... the view just returns to the start.  That has caught a few people out over the years!