Hi ArunRaj, thanks for your post.
I am also hearing complaints on other websites using wp-supersized plugin. I have not seen your site yet, but I have seen that using wp-supersized plugin, along with Google translate, needs special care. I don't think any plugin is to blame here. But a full-size background slider is bound to bog down any site, and adding Google translate complicates this because it first has to detect each individual caption before making a translation.
See this thread for more details about the exact steps in how translations are being made: https://wordpress.org/support/topic/google-language-translator-does-not-work-perfect-in-image-slider-captions?replies=2
The only solution I think is to optimize the speed of your site as much as possible. The faster your website, the faster content should translate. However, Google will always have some delay because of the need to detect each slide caption first, and then making the translation.
I'm sorry that no good solution I cannot provide for this. I hope you continue to use the plugin.
Thanks so much!