One advantage I can imagine is that you can prerender the React components, outputting e.g. plain HTML. With tools like e.g. React Static, that means you can somewhat ergonomically generate different static websites for different languages, avoiding the runtime costs of looking up the correct strings.

Using the Svelte JS library (https://svelte.technology) you can have both: server-side rendered components [1] and compile to web components (custom elements) [2]

Another advantage is that the components compile to vanilla JavaScript, so we don't rely on a runtime library to run the application.

[1] https://svelte.technology/guide#server-side-rendering

[2] https://svelte.technology/guide#custom-elements