Do you use root tabs? Echinodorus are heavy root feeders but can tolerate a fairly wide range of light - although not too bright. Pinch off the transparent leaves but unless you fix the problem the rest will likely go the same way.
Agree with others. Leaves do not regenrate, the plant knows not to waste energy and will produce new leaves (from the centre of the crown), but as has been mentioned these too will waste away unless the nutrient issue is rectified. Substrate tabs are the best form of nutrient supplementation for Echinodorus plants, but they will also bnefit from a comprehensive liquid supplement. Some nutrients are taken up by roots, some exclusively by leaves. Flourish Tabs are the best substrate fertilizer I have found.
My tank is 145 litres I give it seven shots of tropica premium nutrition a week when I do water change. And in the photo you can see how much natural light the tank gets. Then from 4pm until 11pm the LED is switched on. Allwater changes are spot on
How long have you had the plant for?
It looks like it is suffering from heat, which might have happened if you got it recently and the plant was left in a bag in a hot car for a while. This could have happened before you got the plant or when you got it.
Other than that it doesn't look right. If the roots are healthy the plant should produce new leaves.
Substrate fertilizer like Flourish Tabs will most likely solve this, as has been said by several members. Colin's point about heat in transport is well taken, but the past is the past and going forward providing good nutrition to this plant is key.