Can i customize "select an action for text" menu? I have downloaded a dictionary application for my native language and English translation and it can work offline.

But i need it to be seen at the "select an action for text" menu when i select a piece of text on a browser, or an e book reader, or an offline browser.

Is it the business of developer of the dictionary app?

If not how can i add an app to "select an action for text" menu?

Thanks.
Short answer
You yourself cannot. But you can ask the developer to implement that.
TL;DR
Explanation in easy terms: an app itself must &quot;register for this service&quot;, which must be done in code.
The &quot;Share picker&quot; is not handled by apps directly – it's rather the system taking care for that. So it must be made known to the system if an app has something to contribute (or can accept from) here, and if so, for what actions/content types. For example, an URL (link) basically is &quot;normal text&quot; (consisting of characters), so it could be copy/pasted to other &quot;text processing apps&quot; (notepads, word processors, etc.); but it could also be passed to browsers or other link-sharing apps in a specific way. A video makes no sense to be copied into a text-based app, so when &quot;sharing&quot; it you wouldn't like a notepad-type app to be in the share menu (which otherwise would be really cluttered pretty soon).
So an app must &quot;tell&quot; the system what type of &quot;sharing content&quot; it can accept, and it must provide a &quot;standardized interface&quot; for this which the system (or rather its &quot;share&quot; component) then can address.
Additional hints
As your question was for a dictionary-type app: Several other apps support those directly. So e.g. ColorDict (my personal favorite currently) is an online/offline dictionary app directly supported by e.g. Moon+ Reader (my favorite app for reading eBooks – ePub, Mobi, PDF, and more supported). Looking up a term even makes ColorDict blending in seemlessly. So apart from the &quot;standard sharing option&quot; of the system, there are also other ways to achieve things. But again, it's up to the developer to implement this.