Arabic input field

Unfortunately no, I2 Localization doesn't implement custom input fields, it relies on NGUI, Unity UI, TextMesh Pro, etc.

Said that, it could be interesting to have a workaround/component to handle input fields. I will look into this and get back to you.

is there any other way to support this in Unity3D?

One way to quickly handle it in NGUI and TextMeshPro is to override the TextGeneration function so that it applies the RTL fix right before generating the quads used for rendering. That way it can store the regular text (which solves the copy/paste, navigation, etc) but still render correct Arabic texts.
Given that the code for Unity UI is not shipped with Unity (and the repository that has it is not up-to-date), then you will have to create a custom component that do the same the input field does but applies the RTL fix. A way to start this, is by downloading the code from the repository, make a copy of the input field class and change the text generator function.
I will see if I can include that as a new feature. However, the next release is already full of features (you can see that in the roadmap) but I can definitively add it for the release after that.

Thanks for the suggestion!
Frank