https://github.com/ziahamza/webui-aria2 the latest commit on 9 Dec 2018.
This commit solve very problems with more recent version chrome and add more languages.
Is it possible to update the opkg version to the latest?
Sure. Feel free to author the upgrade:
Just figure out the needed change to Makefile and related files, author the changes, compile and test them, and then issue a Pull Request to get your changes accepted to the source repo so that buildbot can compile the updated package for opkg.
OpenWrt is a community effort. Packages need people interested on them to do the upgrades. Apparently there has lately been nobody interested in keeping webui-aria2 updated. @kuoruan was interested in it some years ago, but has not been active with that package lately.