Regarding dictionary lookups:
On second thought, a dedicated (but optional) Wiktionary
button in Marvin might be useful. I've just tried reading a Polish e-book in Marvin. Looking up Polish-English translations in the Collins Polish-English dictionary (within the Lingvo app) works reasonably well:
- tap & hold a word in Marvin
- press the Copy button
- four-finger swipe to the right to open Lingvo
- read the translation there
- four-finger swipe to the left to return to Marvin
However, there is no Polish-Polish dictionary in the Lingvo app... and the only one I found in the App Store is an offline version of the Polish Wiktionary. So, why not make Wiktionary directly accessible from within Marvin? The Polish Wiktionary only contains about 28 thousand terms (while top-notch dictionaries might offer up to 70-100 thousand terms), but it's definitely better than nothing.
Russian or German work particularly well within Lingvo. You can, for example, set up the Collins Russian-English dictionary as the Lingvo default, but Lingvo will automatically show you not just the Russian-English translation of a term, but right below that, also the term's definition from the Russian-Russian dictionary. That's the best of both worlds at a single glance!
And, as Kris mentioned, he might succeed in merging steps no. 2 and 3, above, into a single press of a button.