Failed to call hook 'OnEntityDeath' on plugin 'TrollTax v1.1.0' (NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.TrollTax.GetSendMSG (BasePlayer player, System.String message, System.String arg1, System.String arg2, System.String arg3) [0x00019] in <6306ca09eb9a44248c9d81a327931356>:0
at Oxide.Plugins.TrollTax.RemoveTax (System.UInt64 payer, System.UInt64 taxer) [0x0009b] in <6306ca09eb9a44248c9d81a327931356>:0
at Oxide.Plugins.TrollTax.OnEntityDeath (BaseEntity entity, HitInfo hitInfo) [0x0013f] in <6306ca09eb9a44248c9d81a327931356>:0
at Oxide.Plugins.TrollTax.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x003e1] in <6306ca09eb9a44248c9d81a327931356>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

Looks like your configuration file for the plugin is invalid, might be the same with your oxide/lang file.

Can I replace the oxide/lang file without re-installing all of oxide?

Yes, just delete the desired file and reload the plugin.