C++
===
* Make serialization method naming consistent
* Make proto runtime + generated code free of deprecation warnings
* Moved ShutdownProtobufLibrary() to message_lite.h. For backward compatibility a declaration is still available in stubs/common.h, but users should prefer message_lite.h
* Removed non-namespace macro EXPECT_OK()
* Removed mathlimits.h from stubs in favor of using std::numeric_limits from C++11
* Fixed bug in parser when ending on a group tag
* Add a helper function to UnknownFieldSet to deal with the changing return value of message::unknown_fields()
* Fix incorrect use of string_view iterators
* Support direct pickling of nested messages
* Skip extension tag validation for MessageSet if unknown dependencies are allowed
* Updated deprecation macros to annotate deprecated code (6612)
* Remove conversion warning in MapEntryFuncs::ByteSizeLong (6766)
* Revert "Make shared libraries be able to link to MSVC static runtime libraries, so that VC runtime is not required." (6914)
Java
====
* Remove the usage of MethodHandle, so that Android users prior to API version 26 can use protobuf-java
* Publish ProGuard config for javalite
* Fix for StrictMode disk read violation in ExtensionRegistryLite
* Include part of the ByteString's content in its toString().
* Include unknown fields when merging proto3 messages in Java lite builders
Python
=====
* Add float_precision option in json format printer
* Optionally print bytes fields as messages in unknown fields, if possible
* FieldPath: fix testing IsSet on root path ''
* Experimental code gen (fast import protobuf module) which only work with cpp generated code linked in
JavaScript
========
* Remove guard for Symbol iterator for jspb.Map
PHP
====
* Avoid too much overhead in layout_init (6716)
* Lazily Create Singular Wrapper Message (6833)
* Implement lazy loading of php class for proto messages (6911)
Ruby
====
* Ruby lazy wrappers optimization (6797)
C
==
* (RepeatedField): Capacity property to resize the internal array (6530)
* Experimental proto2 support is now officially available (4642, 5183, 5350, 5936)
* Getting started doc: https://github.com/protocolbuffers/protobuf/blob/master/docs/csharp/proto2.md
* Add length checks to ExtensionCollection (6759)
* Optimize parsing of some primitive and wrapper types (6843)
* Use 3 parameter Encoding.GetString for default string values (6828)
* Change _Extensions property to normal body rather than expression (6856)
Objective C
=========
* Fixed unaligned reads for 32bit arm with newer Xcode versions (6678)